ABSTRACT: OBJECTIVES:To describe the change in physical activity (total, leisure, household, occupational) in men over a mean 5-year follow-up period and to identify sociodemographic and health factors associated with change in physical activity. DESIGN:Prospective cohort study; Osteoporotic Fractures in Men Study; data collected March 2000 through May 2006. SETTING:Six U.S. clinical centers. PARTICIPANTS:Volunteer sample of ambulatory community-dwelling men aged 65 and older (N=5,161). MEASUREMENTS:Self-reported physical activity assessed at baseline and Visit 2 (V2) (5 years apart) according to the Physical Activity Scale for the Elderly (PASE) (unitless, relative measure of physical activity). RESULTS:At baseline, PASE scores averaged 16.8+/-35.5 for occupational, 37.0+/-34.0 for leisure, 95.9+/-43.2 for household, and 149.7+/-67.6 for total physical activity. Occupational (-6.2+/-33.9), leisure (-3.2+/-37.3), household (-9.9+/-44.3), and total (-19.3+/-67.7) physical activity change scores declined, on average, from baseline to V2. On average, change in total PASE scores declined more with age: -15.6+/-71.6 for men younger than 70, -16.4+/-67.0 for men aged 70 to 74, -21.4+/-66.9 for men aged 75 to 79, and -29.5+/-60.7 for men aged 80 and older. Living alone, smoking cigarettes, poor health, and higher blood pressure were associated with greater declines in physical activity over time. Although average scores declined, some older men (1,335, 26%) reported increasing physical activity levels. Better physical and mental health, living with others, and being younger were associated with the probability of increasing physical activity over time. CONCLUSION:Over the 5-year period, the majority of men reported declines in total physical activity. Older men in poor health who live alone have a high risk of physical activity declines and may be an important group to target for exercise interventions.