Increased emphasis on breast conservation and the primacy of the patient's preferences has led to the promotion and increased use of a two-step surgical strategy (definitive operation only after a final tissue diagnosis from a biopsy done on a previous visit) in the treatment of early breast cancer, with the assumption being that this is more conducive to the performance of breast-conserving surgery (BCS). We sought to test this by examining the effect of the surgical strategy (one-step versus two-step) on the operation performed (BCS versus mastectomy). A random sample of women with node-negative breast cancer diagnosed in 1991 in Ontario was drawn from the Ontario Cancer Registry database and matched to the Canadian Institute of Health Information and Ontario Health Insurance Plan databases (n = 643). This provided information on the timing and nature of all surgical procedures performed as well as patient, tumor, hospital, and surgeon characteristics. The surgical strategy was defined as either a one-step procedure (biopsy and definitive surgery performed at the same time) or a two-step procedure (surgical biopsy and pathologic diagnosis, followed by definitive surgery at a later date). The axillary lymph node dissection was used to define the definitive procedure. BCS was employed in 68% of patients, and this did not differ significantly between the one-step and two-step groups (66% versus 70%). Patients with palpable lesions had a significantly lower rate of breast conservation than those with nonpalpable lesions. Other variables associated with a lower rate of BCS were larger tumor size, presence of extensive ductal carcinoma in situ (DCIS), and central or multifocal tumors. The use of a one-step procedure was associated with a patient age of more than 50 years, a palpable mass, tumor size larger than 1 cm, previous fine needle aspiration (FNA) biopsy, absence of extensive DCIS, and surgery in an academic setting. Breast conservation was not affected by the surgical strategy used or the timing of the decision, but was associated with several accepted tumor factors. This study shows that, contrary to the opinion of some, there is a group of breast cancer patients in whom treatment in a one-step manner is appropriate.