Context: Results of prior pathology workforce surveys have varied between a state of equilibrium and predictions of shortage. Objective: To assess the current and future supply of pathologists, and apply a dynamic modeling tool for assessing the effects of changing market forces and emerging technologies on the supply of pathologists' services through 2030. Design: Data came from various sources, including the literature, College of American Pathologists' internal data, and primary research through custom-developed surveys for the membership and for pathology practice managers Results: Through 2010, there were approximately 18 000 actively practicing pathologists in the United States (5.7 per 100 000 population), approximately 93% of whom were board certified. Our model projects that the absolute and per capita numbers of practicing pathologists will decrease to approximately 14 000 full-time equivalent (FTE) pathologists or 3.7 per 100 000 in the coming 2 decades. This projection reflects that beginning in 2015, the numbers of pathologists retiring will increase precipitously, and is anticipated to peak by 2021. Including all types of separation, the net pathologist strength will begin falling by year 2015. Unless workforce entry or exit rates change, this trend will continue at least through 2030. These changes reflect the closure of many training programs 2 to 4 decades ago and the substantially decreased number of graduating residents. Conclusions: This comprehensive analysis predicts that pathologist numbers will decline steadily beginning in 2015. Anticipated population growth in general and increases in disease incidence owing to the aging population, to be presented in a companion article on demand, will lead to a net deficit in excess of more than 5700 FTE pathologists. To reach the projected need in pathologist numbers of nearly 20 000 FTE by 2030 will require an increase from today of approximately 8.1% more residency positions. We believe a pathologist shortage will negatively impact both patient access to laboratory services and health care providers' abilities to deliver more effective health care to their patient populations.