The study aimed to describe the surgical treatment in cases of primary, operable breast cancer in Victoria. All patients who were entered in a population-based cancer registry and who met the entry criteria over a six-month period were identified. In respect of each patient, the treating surgeon completed a questionnaire about patient characteristics, investigations, tumour description, surgery, radiotherapy and chemotherapy. For 716 eligible cases, 635 (89%) questionnaires were returned by 200 treating surgeons; this gave a mean rate of 6.3 breast-cancer patients per surgeon per year. Most (61%) surgeons treated one to four breast-cancer patients per year and only 4% of surgeons treated more than 20 breast-cancer patients each. Little systematic difference was found in the treatment approach that was adopted by the surgeons with heavy or light case-loads of patients with breast cancer. Twenty-two per cent of patients underwent breast-conserving operations. Virtually all the remainder underwent mastectomy, most commonly modified radical mastectomy.