To examine physician and patient characteristics related to the ordering of imaging studies in a general medicine practice and to determine whether physician gender influences ordering patterns. Retrospective cohort study. Hospital-based academic general medicine practice of 29 attending physicians. All 8,203 visits by 5.011 patients during a 6-month period. For each visit the following variables were abstracted from the electronic patient record: patient age, patient gender, visit urgency, visit type, and physician seen. All diagnostic imaging studies performed within 30 days of each outpatient visit were identified from the hospital's Radiology Information System. Screening mammography was not included in the analysis. Physician variables included gender and years since medical school graduation. Logistic regression analysis was used to evaluate the effect of various patient, physician, and visit characteristics on the probability of a diagnostic imaging study being ordered. Patient age, urgent visits, visit frequency, and the gender of the physician were all significantly related to the ordering of an imaging study. Correcting for all other factors, the ordering of an imaging study during an outpatient medical visit was 40% more likely if the physician was female (odds ratio=1.40; 95% confidence interval [CI] 1.01, 1.95). Female physicians were 62% more likely (95% CI 0.99, 2.64) than male physicians to order an imaging study for a male patient and 21% more likely (95% CI 0.87, 1.69) to order an imaging study for a female patient. Physician gender is a predictor of whether an outpatient medical visit generates an imaging study. Reasons for this observation are unclear, but may be the result of different pratice styles of male and female physicians or unmeasured patient characteristics.