May be a little roundabout, but this seems to work for me:
<font face=Tahoma><SPAN style="color:#00007F">Sub</SPAN> test()
<SPAN style="color:#00007F">Dim</SPAN> dataRange <SPAN style="color:#00007F">As</SPAN> Range, dataCount <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Integer</SPAN>, cellsCount <SPAN style="color:#00007F">As</SPAN> <SPAN style="color:#00007F">Integer</SPAN>
<SPAN style="color:#007F00">'This is the range to check</SPAN>
<SPAN style="color:#00007F">Set</SPAN> dataRange = Selection
<SPAN style="color:#007F00">'This counts the number of cells in the range</SPAN>
cellsCount = dataRange.Cells.Count
<SPAN style="color:#007F00">'This counts the number of cells in the range that are not empty</SPAN>
dataCount = WorksheetFunction.CountA(dataRange)
<SPAN style="color:#00007F">If</SPAN> cellsCount = dataCount <SPAN style="color:#00007F">Then</SPAN> <SPAN style="color:#007F00">'if the counts match then...</SPAN>
<SPAN style="color:#007F00">'your code here (true)</SPAN>
<SPAN style="color:#00007F">Else</SPAN>
<SPAN style="color:#007F00">'your code here (false)</SPAN>
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">If</SPAN>
<SPAN style="color:#00007F">End</SPAN> <SPAN style="color:#00007F">Sub</SPAN></FONT>