OBJECTIVES: Our goal was to determine if increasing primary care physician supply was associated with lower incidence and mortality rates for colorectal cancer. STUDY DESIGN: We performed an ecologic study of Florida's 67 counties, using data from the state tumor registry and the American Medical Association physician masterfile. POPULATION: Florida residents were included. OUTCOMES MEASURED: We measured age-adjusted colorectal cancer incidence and mortality rates for Florida's 67 counties during the period 1993 to 1995. RESULTS: Increasing primary care physician supply was negatively correlated with both colorectal cancer (CC) incidence (CC = -0.46; P < .0001) and mortality rates (CC = -0.29; P =.02). In linear regression that controlled for other county characteristics, each 1% increase in the proportion of county physicians who were in primary care specialties was associated with a corresponding reduction in colorectal cancer incidence of 0.25 cases per 100,000 (P < .0001) and a reduction in colorectal cancer mortality of 0.08 cases per 100,000 (P =.0008). CONCLUSIONS: Incidence and mortality of colorectal cancer decreased in Florida counties that had an increased supply of primary care physicians. This suggests that a balanced work force may achieve better health outcomes.