BACKGROUND: Predicting future general practitioner workforce requires information about how demographic factors affect GP workforce participation. Regional differences might not be accounted for in national studies. The authors aimed to determine GP characteristics associated with workforce participation in Tasmania. METHODS: A self administered census of Tasmanian GPs measured GP demographics and the number of 3.5 hour sessions worked in 1 week in 2005. RESULTS: Four hundred and three GPs responded (76% response rate). Six percent of GPs were on leave at the time of the census. Age, gender and graduation outside of Australia, the United Kingdom or Ireland were associated with workforce participation, but rurality had no effect. The effect of age was modified by gender with women aged over 55 years being more likely to work full time (p=0.03). DISCUSSION: Factors affecting workforce participation may vary across regions. Predictions based on national models may need to be interpreted in the context of local circumstances.