diff --git a/examples/example-grouping.html b/examples/example-grouping.html
index 86bbd4a9b..356ade7d6 100644
--- a/examples/example-grouping.html
+++ b/examples/example-grouping.html
@@ -170,7 +170,8 @@ <h2>View Source:</h2>
       new Slick.Data.Aggregators.Avg("percentComplete"),
       new Slick.Data.Aggregators.Sum("cost")
     ],
-    aggregateCollapsed: false
+    aggregateCollapsed: false,
+    lazyTotalsCalculation: true
   });
 }
 
@@ -187,7 +188,8 @@ <h2>View Source:</h2>
       new Slick.Data.Aggregators.Avg("percentComplete"),
       new Slick.Data.Aggregators.Sum("cost")
     ],
-    aggregateCollapsed: aggregateCollapsed
+    aggregateCollapsed: aggregateCollapsed,
+    lazyTotalsCalculation: true
   });
 }
 
@@ -202,7 +204,8 @@ <h2>View Source:</h2>
         new Slick.Data.Aggregators.Sum("duration"),
         new Slick.Data.Aggregators.Sum("cost")
       ],
-      aggregateCollapsed: true
+      aggregateCollapsed: true,
+      lazyTotalsCalculation: true
     },
     {
       getter: "effortDriven",
@@ -213,7 +216,8 @@ <h2>View Source:</h2>
         new Slick.Data.Aggregators.Avg("percentComplete"),
         new Slick.Data.Aggregators.Sum("cost")
       ],
-      collapsed: true
+      collapsed: true,
+      lazyTotalsCalculation: true
     }
   ]);
 }
@@ -229,7 +233,8 @@ <h2>View Source:</h2>
         new Slick.Data.Aggregators.Sum("duration"),
         new Slick.Data.Aggregators.Sum("cost")
       ],
-      aggregateCollapsed: true
+      aggregateCollapsed: true,
+      lazyTotalsCalculation: true
     },
     {
       getter: "effortDriven",
@@ -239,7 +244,8 @@ <h2>View Source:</h2>
       aggregators :[
         new Slick.Data.Aggregators.Sum("duration"),
         new Slick.Data.Aggregators.Sum("cost")
-      ]
+      ],
+      lazyTotalsCalculation: true
     },
     {
       getter: "percentComplete",
@@ -250,7 +256,8 @@ <h2>View Source:</h2>
         new Slick.Data.Aggregators.Avg("percentComplete")
       ],
       aggregateCollapsed: true,
-      collapsed: true
+      collapsed: true,
+      lazyTotalsCalculation: true
     }
   ]);
 }
@@ -265,7 +272,7 @@ <h2>View Source:</h2>
     d["id"] = "id_" + i;
     d["num"] = i;
     d["title"] = "Task " + i;
-    d["duration"] = Math.round(Math.random() * 14);
+    d["duration"] = Math.round(Math.random() * 30);
     d["percentComplete"] = Math.round(Math.random() * 100);
     d["start"] = someDates[ Math.floor((Math.random()*2)) ];
     d["finish"] = someDates[ Math.floor((Math.random()*2)) ];
diff --git a/slick.core.js b/slick.core.js
index 48a041643..2f097b1db 100644
--- a/slick.core.js
+++ b/slick.core.js
@@ -370,6 +370,14 @@
      * @type {Group}
      */
     this.group = null;
+
+    /***
+     * Whether the totals have been fully initialized / calculated.
+     * Will be set to false for lazy-calculated group totals.
+     * @param initialized
+     * @type {Boolean}
+     */
+    this.initialized = false;
   }
 
   GroupTotals.prototype = new NonDataItem();
diff --git a/slick.dataview.js b/slick.dataview.js
index 3c3d2042a..c6389f507 100644
--- a/slick.dataview.js
+++ b/slick.dataview.js
@@ -60,7 +60,8 @@
       aggregateCollapsed: false,
       aggregateChildGroups: false,
       collapsed: false,
-      displayTotalsRow: true
+      displayTotalsRow: true,
+      lazyTotalsCalculation: false
     };
     var groupingInfos = [];
     var groups = [];
@@ -363,7 +364,22 @@
     }
 
     function getItem(i) {
-      return rows[i];
+      var item = rows[i];
+
+      // if this is a grou row, make sure totals are calculated and update the title
+      if (item && item.__group && item.totals && !item.totals.initialized) {
+        var gi = groupingInfos[item.level];
+        if (!gi.displayTotalsRow) {
+          calculateTotals(item.totals);
+          item.title = gi.formatter ? gi.formatter(item) : item.value;
+        }
+      }
+      // if this is a totals row, make sure it's calculated
+      else if (item && item.__groupTotals && !item.initialized) {
+        calculateTotals(item);
+      }
+
+      return item;
     }
 
     function getItemMetadata(i) {
@@ -421,7 +437,7 @@
      * @param varArgs Either a Slick.Group's "groupingKey" property, or a
      *     variable argument list of grouping values denoting a unique path to the row.  For
      *     example, calling collapseGroup('high', '10%') will collapse the '10%' subgroup of
-     *     the 'high' setGrouping.
+     *     the 'high' group.
      */
     function collapseGroup(varArgs) {
       var args = Array.prototype.slice.call(arguments);
@@ -437,7 +453,7 @@
      * @param varArgs Either a Slick.Group's "groupingKey" property, or a
      *     variable argument list of grouping values denoting a unique path to the row.  For
      *     example, calling expandGroup('high', '10%') will expand the '10%' subgroup of
-     *     the 'high' setGrouping.
+     *     the 'high' group.
      */
     function expandGroup(varArgs) {
       var args = Array.prototype.slice.call(arguments);
@@ -503,27 +519,50 @@
       return groups;
     }
 
-    // TODO:  lazy totals calculation
-    function calculateGroupTotals(group) {
-      // TODO:  try moving iterating over groups into compiled accumulator
+    function calculateTotals(totals) {
+      var group = totals.group;
       var gi = groupingInfos[group.level];
       var isLeafLevel = (group.level == groupingInfos.length);
-      var totals = new Slick.GroupTotals();
       var agg, idx = gi.aggregators.length;
+
+      if (!isLeafLevel && gi.aggregateChildGroups) {
+        // make sure all the subgroups are calculated
+        var i = group.groups.length;
+        while (i--) {
+          if (!group.groups[i].initialized) {
+            calculateTotals(group.groups[i]);
+          }
+        }
+      }
+
       while (idx--) {
         agg = gi.aggregators[idx];
         agg.init();
-        gi.compiledAccumulators[idx].call(agg,
-            (!isLeafLevel && gi.aggregateChildGroups) ? group.groups : group.rows);
+        if (!isLeafLevel && gi.aggregateChildGroups) {
+          gi.compiledAccumulators[idx].call(agg, group.groups);
+        } else {
+          gi.compiledAccumulators[idx].call(agg, group.rows);
+        }
         agg.storeResult(totals);
       }
+      totals.initialized = true;
+    }
+
+    function addGroupTotals(group) {
+      var gi = groupingInfos[group.level];
+      var totals = new Slick.GroupTotals();
       totals.group = group;
       group.totals = totals;
+      if (!gi.lazyTotalsCalculation) {
+        calculateTotals(totals);
+      }
     }
 
-    function calculateTotals(groups, level) {
+    function addTotals(groups, level) {
       level = level || 0;
       var gi = groupingInfos[level];
+      var groupCollapsed = gi.collapsed;
+      var toggledGroups = toggledGroupsByLevel[level];      
       var idx = groups.length, g;
       while (idx--) {
         g = groups[idx];
@@ -532,38 +571,20 @@
           continue;
         }
 
-        // Do a depth-first aggregation so that parent setGrouping aggregators can access subgroup totals.
+        // Do a depth-first aggregation so that parent group aggregators can access subgroup totals.
         if (g.groups) {
-          calculateTotals(g.groups, level + 1);
+          addTotals(g.groups, level + 1);
         }
 
         if (gi.aggregators.length && (
             gi.aggregateEmpty || g.rows.length || (g.groups && g.groups.length))) {
-          calculateGroupTotals(g);
+          addGroupTotals(g);
         }
-      }
-    }
 
-    function finalizeGroups(groups, level) {
-      level = level || 0;
-      var gi = groupingInfos[level];
-      var groupCollapsed = gi.collapsed;
-      var toggledGroups = toggledGroupsByLevel[level];
-      var idx = groups.length, g;
-      while (idx--) {
-        g = groups[idx];
         g.collapsed = groupCollapsed ^ toggledGroups[g.groupingKey];
         g.title = gi.formatter ? gi.formatter(g) : g.value;
-
-        if (g.groups) {
-          finalizeGroups(g.groups, level + 1);
-          // Let the non-leaf setGrouping rows get garbage-collected.
-          // They may have been used by aggregates that go over all of the descendants,
-          // but at this point they are no longer needed.
-          g.rows = [];
-        }
       }
-    }
+    } 
 
     function flattenGroupedRows(groups, level) {
       level = level || 0;
@@ -793,8 +814,7 @@
       if (groupingInfos.length) {
         groups = extractGroups(newRows);
         if (groups.length) {
-          calculateTotals(groups);
-          finalizeGroups(groups);
+          addTotals(groups);
           newRows = flattenGroupedRows(groups);
         }
       }