The MW 6.1 earthquake of 4 September 1963 is the largest earthquake known to have occurred in the highly active seismic zone along the east coast of Baffin Island. Previous efforts to study this earthquake employed different subsets of the available data and did not reach a consensus regarding the focal mechanism, although all agree that there was a significant component of normal slip involved. The present study makes use of all the waveform data used by previous authors, as well as additional seismograms that were either unused (mainly southern Canadian data) or unavailable (data from the former Soviet Union) in the past. The preferred focal mechanism based on waveform modeling implies nearly pure normal faulting on a roughly east-west striking plane. This solution is compatible with both the regional and teleseismic body wave data and is similar to some of the previously suggested mechanisms. The focal mechanism also appears to be consistent with the aftershock distribution. This and previous studies are in agreement with regard to the depth (7 km) and size (MW 6.1) of the earthquake.