Incomplete understanding of attrition from the physician workforce has hampered policy-makers’ efforts to achieve optimal alignment of the supply of physicians with population demand for medical services. This longitudinal study of Ontario primary care physicians uses health administrative data to characterize changes in physicians’ practice patterns over time. We examined the workload and scopes of practice of 21,240 physicians between 1992 and 2013. We found that physicians reduce their workloads gradually as they age, retiring from clinical practice at an average age of 70.5. Furthermore, we found that 60% of family physicians who stop providing comprehensive primary care continue to provide clinical services for an average of three years, with reduced workloads, before retiring fully. Our findings clarify the process of physician attrition from the workforce and will help to improve estimates of attrition and make physician workforce planning more accurate and effective.