OBJECTIVE To investigate workforce participation patterns among Australian medical graduates and the extent of cohort differences in these patterns. DESIGN We carried out a retrospective longitudinal cohort study, with data collected by postal survey on current occupation, location, absences from the workforce and occupation since graduation. PARTICIPANTS Graduates who had completed their basic medical training at Monash University, Melbourne, Australia, in 1980, 1985, 1990 and 1995 were invited to participate (n = 546); 368 took part in the study (69%). OUTCOME MEASURES The proportion of graduates in the Australian medical workforce, the equivalent full-time contribution to the Australian medical workforce, and the proportion taking temporary absences from the workforce were determined. RESULTS The rate of participation in the Australian medical workforce was 96% 2 years after graduation. It then declined to reach 85% by 10 years and regained slightly to reach 88% by 15 years after graduation. There was no indication that the 1995 cohort made a lower contribution to the Australian medical workforce than the earlier cohorts in their first 7 years after graduation. CONCLUSION Although there are few indications of differences between these cohorts during the first 7 years after graduation, the main contributing factors to losses from the Australian medical workforce - medical work overseas and parental leave - do not exert their maximum influence until a later timepoint. Longitudinal cohort data are essential for monitoring trends in medical workforce participation and hence for effective workforce planning.