The objective of this article was to examine whether characteristics of referring physicians and their practice environment were associated with surgical referral behavior for early-stage breast cancer patients. A total of 2801 women diagnosed with early-stage breast cancer and their referring physicians were identified from the Iowa Surveillance, Epidemiology, and End Results (SEER) database during 1989-1996. The Iowa Physician Inventory was used to collect information on characteristics of referring physicians. Multiple logistic regression analyses were conducted to evaluate characteristics of the referring physicians and their practice environment to explain surgical referral behavior. Affiliation with physicians' networks and professional diversity among area specialists were associated with increased referrals to surgeons more likely to perform breast-conserving surgery. Promoting interaction among physicians, particularly among those with different specialties, may increase the diffusion of new behaviors into clinical practice.