diff --git a/Code/Mantid/Framework/Algorithms/src/MuonGroupDetectors.cpp b/Code/Mantid/Framework/Algorithms/src/MuonGroupDetectors.cpp
index 510bdbb28c5a..86c796e861e7 100644
--- a/Code/Mantid/Framework/Algorithms/src/MuonGroupDetectors.cpp
+++ b/Code/Mantid/Framework/Algorithms/src/MuonGroupDetectors.cpp
@@ -90,7 +90,8 @@ namespace Algorithms
     if ( table->getColumn(2)->type() != "vector_int" )
       throw std::invalid_argument("Invalid type of the third column. Should be vector of ints.");
 
-    size_t numGroups(0);
+    std::vector<size_t> groupRows; // Rows with non-empty groups
+    groupRows.reserve(table->rowCount()); // Most of rows will be groups
 
     // First pass to determine how many non-empty groups we have
     for ( size_t row = 0; row < table->rowCount(); ++row )
@@ -98,19 +99,52 @@ namespace Algorithms
       std::string& itemName = table->cell<std::string>(row, 0);
       std::vector<int>& elements = table->cell< std::vector<int> >(row, 2);
 
-      if ( itemName  == "Group" && elements.size() != 0 )
-      {
-        numGroups++;
-      }
+      if ( itemName == "Group" && elements.size() != 0 )
+        groupRows.push_back(row);
+
     }
 
-    if ( numGroups == 0 )
+    if ( groupRows.size() == 0 )
       throw std::invalid_argument("Detector Grouping Table doesn't contain any non-empty groups");
 
     MatrixWorkspace_sptr inWS = getProperty("InputWorkspace");
 
     // Create output workspace with all the same parameters as an input one except number of histograms
-    MatrixWorkspace_sptr outWS = WorkspaceFactory::Instance().create(inWS, numGroups);
+    MatrixWorkspace_sptr outWS = WorkspaceFactory::Instance().create( inWS, groupRows.size() );
+
+    // Compile the groups
+    for ( auto groupIt = groupRows.begin(); groupIt != groupRows.end(); ++groupIt )
+    {    
+      size_t groupIndex = static_cast<size_t>( std::distance(groupRows.begin(),groupIt) );
+
+      // Not "detectors" as such, but workspace indices. For Muons there is only one detector for
+      // workspace index in the data before grouping.
+      std::vector<int>& detectors = table->cell< std::vector<int> >(*groupIt,2);
+
+      // We will be setting them anew
+      outWS->getSpectrum(groupIndex)->clearDetectorIDs();
+
+      for(auto detIt = detectors.begin(); detIt != detectors.end(); detIt++)
+      {
+        for( size_t i = 0; i < inWS->blocksize(); ++i )
+        {
+          // Sum the y values
+          outWS->dataY(groupIndex)[i] += inWS->dataY(*detIt)[i];
+
+          // Sum the errors in quadrature
+          outWS->dataE(groupIndex)[i] = 
+            sqrt(pow(outWS->dataE(groupIndex)[i], 2) + pow(inWS->dataE(*detIt)[i], 2));
+        }
+
+        // Detectors list of the group should contain all the detectors of it's elements
+        outWS->getSpectrum(groupIndex)->addDetectorIDs( inWS->getSpectrum(*detIt)->getDetectorIDs() );
+      }
+
+      // Using the first detector X values
+      outWS->dataX(groupIndex) = inWS->dataX(detectors.front());
+
+      outWS->getSpectrum(groupIndex)->setSpectrumNo( static_cast<specid_t>(groupIndex + 1) );
+    }
 
     setProperty("OutputWorkspace", outWS);
   }
diff --git a/Code/Mantid/Framework/Algorithms/test/MuonGroupDetectorsTest.h b/Code/Mantid/Framework/Algorithms/test/MuonGroupDetectorsTest.h
index 767051c33f64..8d1bce31171d 100644
--- a/Code/Mantid/Framework/Algorithms/test/MuonGroupDetectorsTest.h
+++ b/Code/Mantid/Framework/Algorithms/test/MuonGroupDetectorsTest.h
@@ -10,6 +10,7 @@
 
 using Mantid::Algorithms::MuonGroupDetectors;
 
+using namespace Mantid;
 using namespace Mantid::Kernel;
 using namespace Mantid::API;
 using namespace Mantid::DataObjects;
@@ -36,6 +37,7 @@ class MuonGroupDetectorsTest : public CxxTest::TestSuite
     const std::string outWSName("MuonGroupDetectorsTest_OutputWS");
 
     MatrixWorkspace_sptr inWS = WorkspaceCreationHelper::Create2DWorkspace123(5,3);
+
     TableWorkspace_sptr grouping = createDetectorGroupingTable(); 
 
     MuonGroupDetectors alg;
@@ -47,14 +49,34 @@ class MuonGroupDetectorsTest : public CxxTest::TestSuite
     TS_ASSERT_THROWS_NOTHING( alg.execute(); );
     TS_ASSERT( alg.isExecuted() );
     
-    // Retrieve the workspace from data service. TODO: Change to your desired type
     MatrixWorkspace_sptr ws;
     TS_ASSERT_THROWS_NOTHING( ws = AnalysisDataService::Instance().retrieveWS<MatrixWorkspace>(outWSName) );
     TS_ASSERT(ws);
 
     if ( ws )
     {
-      TSM_ASSERT( "You forgot to check the results!", 0);
+      TS_ASSERT_EQUALS( ws->getNumberHistograms(), 2);
+      TS_ASSERT_EQUALS( ws->blocksize(), 3 );
+
+      TS_ASSERT_EQUALS( ws->readY(0)[0], 4 );
+      TS_ASSERT_EQUALS( ws->readY(1)[0], 6 );
+
+      TS_ASSERT_EQUALS( ws->readX(0)[1], 1 );
+      TS_ASSERT_EQUALS( ws->readX(1)[1], 1 );
+
+      TS_ASSERT_DELTA( ws->readE(0)[2], 4.243, 0.001);
+      TS_ASSERT_DELTA( ws->readE(1)[2], 5.196, 0.001);
+
+      TS_ASSERT_EQUALS( ws->getSpectrum(0)->getSpectrumNo(), 1);
+      TS_ASSERT_EQUALS( ws->getSpectrum(1)->getSpectrumNo(), 2);
+
+      std::set<detid_t> d1;
+      d1.insert(0); d1.insert(1);
+      TS_ASSERT_EQUALS( ws->getSpectrum(0)->getDetectorIDs(), d1 );
+
+      std::set<detid_t> d2;
+      d2.insert(2); d2.insert(3); d2.insert(4);
+      TS_ASSERT_EQUALS( ws->getSpectrum(1)->getDetectorIDs(), d2 );
     }
     
     // Remove workspace from the data service.
@@ -77,7 +99,7 @@ class MuonGroupDetectorsTest : public CxxTest::TestSuite
     row1 << "Group" << "1" << group1;
 
     std::vector<int> group2;
-    group2.push_back(2); group2.push_back(2); group2.push_back(3);
+    group2.push_back(2); group2.push_back(3); group2.push_back(4);
     TableRow row2 = t->appendRow();
     row2 << "Group" << "2" << group2;