Although medical specialists primarily work full-time, part-time work is on the increase, a trend that can be found worldwide. This article seeks to answer the question why some medical specialists work part-time, while others do not although they are willing to work part-time. Two approaches are used. First, we studied reported reasons and as a second approach we used a theoretical model, based on goal-directed behavior and restrictions. A questionnaire was sent to all internists (N=817), surgeons (N=693) and radiologists (N=621) working in general hospitals in The Netherlands. Questions were asked about personal traits, characteristics of the work situation, and motives for working full-time or part-time. Frequencies were reported for the reasons given, and multilevel analysis was used to test the theoretical model. The results show that the reported reasons for working part-time and being willing to work part-time are the same: the importance of family and leisure pursuits. The second approach showed that medical specialists working part-time tend to be female, older, and have children below the age of five. Surgeons are least likely to work part-time. A willingness to work part-time is purely individual and not related to any of the explanatory variables. We conclude that working part-time is related to both professional and personal circumstances. Policy should be aimed at removing the organizational difficulties that obstruct the realization of part-time work. Alternatively, perhaps there should be a change in working hours for all medical specialists. As the majority of all full-time working medical specialists are willing to work part-time, this might indicate that most medical specialists actually prefer "normal" working hours.