Theoretically, those classified by the Bureau of Labor Statistics as involuntary part-time workers are individuals who would like to work full-time but have been unable to obtain full-time employment. To empirically test the accuracy of that definition, the author employs simple probit models of employment preferences and employment opportunities estimated with data from the March 1990 Current Population Survey. The results confirm that those classified as involuntary part-time workers were indeed employed part-time “involuntarily.” Furthermore, those classified as involuntary part-time workers in 1990 were at least 50% more likely to be in the full-time labor force in 1991 than were those who were classified as voluntary part-time workers in 1990.