Identifying physician and patient characteristics is important in implementing effective, targeted strategies to improve breast cancer detection rates through increased screening recommendations and uptake. The purpose of this study was to determine whether Ontario physicians recommend breast screening using mammography every 2 years for women aged 50-69 as encouraged by the Ontario Breast Screening Program. This study also aimed to identify physician and patient characteristics that may influence adherence to these recommendations. The study design was a cross-sectional study. Using the Canadian Medical Directory-Ontario database, 3063 questionnaires were mailed to all active general and family practitioners. A response rate of 38% (N = 939) was achieved. Adherence to screening was defined as recommending screening to women aged 50-69 only, every 2 years as outlined by the Ontario Breast Screening Program. Bivariate analyses and unconditional logistic regression were used to assess physician adherence to screening guidelines. Only 38.9% of physicians followed recommended breast screening guidelines. After adjusting for physician sex and age, predictors of screening adherence include physicians working in academic or research centers (odds ratio 8.3, 95% confidence interval 1.7-39.7) and those reporting that over 31% of their patients to be of low-income (odds ratio 1.6, 95% confidence interval 1.1-2.4). Compared with physicians working in a rural/town setting (<10 000 people), those located in a large city (>100 000 people) were less likely to adhere to screening guidelines (odds ratio 0.5, 95% confidence interval 0.3-0.7). A low proportion of Ontario physicians adhere to recommended breast screening guidelines. Future research into effective strategies to increase adherence should take into account practice location, setting and patient characteristics.