While the effects of physician organization have been examined extensively, little is known about factors related to physicians' choice of either the solo or group practice setting. This study develops a model of physician practice mode choice that includes variables measuring both the characteristics of individual physicians and the socioeconomic environment. The analysis is stratified by 9 specialty groupings to allow a comparison of inter-specialty differences in practice mode choice. Findings suggest that, in general, the group practice physician tends to be board-certified, a member of the American Medical Association (AMA), younger than 55 years old and a graduate of a U.S. medical school. In addition to this general profile, substantial differences exist by specialty. A number of environmental factors are also shown to be related to the practice mode decision. Finally, results are discussed in relation to trends in the health care field and possible effects on the future distribution of group versus solo practice physicians.