Studies on the association between physical activity and fatal prostate cancer have produced inconclusive results. The Puerto Rico Heart Health Program was a cohort study of a randomly selected sample of 9824 men age 35 to 79 years at baseline who were followed for mortality until 2002. Multiple examinations collected information on lifestyle, diet, body composition, exercise, urban-rural residence, and smoking habits. Physical activity status was measured using the Framingham Physical Activity Index, an assessment of occupational, leisure-time, and other physical activities measured as usual activity over the course of a 24-hour day. Physical activity was stratified into quartiles. Multivariate logistic regression analysis was used to assess the association of physical activity with prostate cancer mortality. Other covariates included age, education, urban-rural residence, smoking, and body mass index. Compared with the lowest level of physical activity (Q1), the risk of prostate cancer mortality was OR = 0.99 (95% CI = 0.64-1.55) for Q2, OR = 1.34 (95% CI = 0.88-2.05) for Q3, and OR = 1.19 (95% CI = 0.75-1.90) for Q4. Further analyses by age group, overweight status, or vigorous physical activity also did not show a significant association between physical activity and prostate cancer mortality. Physical activity did not predict prostate cancer mortality in this group of Puerto Rican men.