Background: Despite accumulating evidence about the harm of polypharmacy in family medicine, few studies have investigated factors related to polypharmacy. The objective of this study was to explore factors related to physicians' prescribing behavior.Methods: We conducted a survey of physicians at 5 family medicine residency practices and a linked health record review of their patients >65 years old. The determinants of physicians' mean number of prescriptions and potentially inappropriate medications (PIMs) were examined using a generalized linear model.Results: A total of 61 physicians (38 residents, 23 fellows/faculty) completed the survey, and 2103 visits by 932 patients seen by these physicians were analyzed. The mean numbers of prescriptions and PIMs per visit per physician were 9.50 and 0.46, respectively. After controlling for patient race and age, low prescribers were more likely to consider the number of medications (P ؍ .007) and benefit/risk information for deprescribing (P ؍ .017) when making prescribing decisions. Use of the Beers List was marginally significant in lower PIM prescribing (P ؍ .05). Physicians' sex, duration of experience, and perceived confidence were not associated with prescribing patterns.Conclusions: Conscious consideration concerning the number of medications and benefit/risk information, as well as using the Beers List, were associated with less polypharmacy and fewer PIMs. (J Am Board Fam Med 2017;30:528 -536.)