Primary care physicians (PCPs) are assuming greater roles in cancer risk assessment and susceptibility testing of patients. The objective of this study was to assess the beliefs and practices of PCPs relative to genetic susceptibility testing for cancer. A cross-sectional survey was mailed to 726 PCPs in community-based practices in southeastern Pennsylvania and southern New Jersey. Data were collected on physician background, cognitive and psychosocial factors, practice environment, and patient factors. The main outcome measure was physician self-reported recommendation or referral of patients for cancer genetic susceptibility testing in a 12-month period prior to the survey. Of those surveyed, 475 (65%) PCPs responded. Complete survey data were available for 433 PCPs. Multivariable analyses show that factors positively associated with PCP recommendation/referral included: patient inquiry about their need for genetic testing for cancer (p < 0.001); PCP belief that patient age is the best predictor of cancer risk (p = 0.01); PCP self-reported frequency of collecting patient diet information (p = 0.01) and medical history information (p = 0.01); and PCP participation in an integrated health system (p = 0.01). PCP use of cancer genetic susceptibility testing may be influenced by patient inquiry, provider beliefs about factors that affect cancer risk, provider collection of risk-assessment data, and provider practice environment.