BACKGROUND Primary care physicians are ideally positioned to affect a large population at risk for epidemics of sedentary lifestyle; however, it is unclear what type of counseling they provide. METHODS A questionnaire was used to obtain information on primary care physicians' behaviors with respect to counseling and prescribing physical activity, physician demographics, and practice characteristics. Registered primary care physicians in Canada were contacted in all 10 provinces and 2 territories. RESULTS Of 27 980 primary care physicians, 14 319 returned usable questionnaires and 13 166 were eligible for study participation (response rate, 51.2%). Respondents were predominantly male (61.1%), practiced in private office/clinic settings (73.4%), and had graduated from medical school more than 22 years earlier. Eighty-five percent of respondents reported asking patients about their physical activity levels, whereas only 26.2% assessed patient fitness as part of a physical examination or through a fitness test and only 10.9% referred patients to others for fitness assessment or appraisal. Most physicians (69.8%) reported using verbal counseling to promote physical activity, whereas only 15.8% used written prescriptions for a physical activity promotion program. Male and female physicians responded differently. Men more frequently assessed fitness than did women, whereas women more frequently asked and provided verbal and written directions. CONCLUSIONS This large sample of Canadian primary care physicians regularly asked patients about physical activity levels and advised them using verbal counseling. Few respondents provided written prescriptions, performed fitness assessments, or referred patients. These results suggest possible opportunities to improve physicians' counseling and prescription efforts.