Sedentary behavior among older adults increases risk for chronic diseases. Physicians in a primary care setting can play an important role in promoting physical activity adoption among their older patients. The Physically Active for Life (PAL) project was a randomized, controlled trial comparing the efficacy of brief physician-delivered physical activity counseling to usual care on self-reported physical activity levels. The physical activity counseling was based on the Transtheoretical Model of Change and social learning theory. Twenty-four community-based primary care medical practices were recruited into the study; 12 were randomized to the Intervention condition and 12 to the Control condition. Physicians in the Intervention practices received training in the delivery of brief physical activity counseling. Subjects in the Intervention practices (n=181) received brief activity counseling matched to their stage of motivational readiness for physical activity, a patient manual, a follow-up appointment with their physician to discuss activity counseling, and newsletter mailings. Subjects in the Control practices (n=174) received standard care. Measures of motivational readiness for physical activity and the Physical Activity Scale for the Elderly (PASE) were administered to subjects in both conditions at baseline, 6 weeks following their initial appointment, and at 8 months. Results showed that at the 6-week follow-up, subjects in the Intervention condition were more likely to be in more advanced stages of motivational readiness for physical activity than subjects in the Control condition. This effect was not maintained at the 8 month follow-up and the intervention did not produce significant changes in PASE scores. Results suggest that more intensive, sustained interventions may be necessary to promote the adoption of physical activity among sedentary, middle-aged, and older adults in primary care medical practices.