BACKGROUND The aim of this study was to compare the outcomes of bilateral breast carcinoma (BBC) patients with those of patients who had unilateral disease. METHODS From 1960 to 1995, 1465 Stage 0–III patients with primary breast carcinoma were treated with either mastectomy or breast conservation therapy at the Kimmel Cancer Center of Jefferson Medical College and Thomas Jefferson University Hospital. There were 1315 (89.9%) unilateral, 103 (7.1%) metachronous, and 47 (3.0%) synchronous breast carcinoma patients. Patients with synchronous breast carcinoma were defined as having a contralateral cancer diagnosed within 1 year of initial diagnosis. The percentage of patients with Stage 0–I disease at initial diagnosis was 49.4%, whereas 68% had Stage 0–I disease at subsequent diagnosis. For patients with metachronous breast carcinomas, the median interval between the first and second diagnosis was 44 months (range, 13–287 months). The median follow‐up time was 58 months (range, 12–229 months) for patients with synchronous cancers and 87 months (range, 0.25–414 months) for those with metachronous cancers. Rates of overall survival and survival with no evidence of disease (NED survival), local control, and distant metastasis from the time of the second diagnosis were calculated for patients with synchronous and metachronous disease. These figures were then compared with each other and also with those for unilateral breast carcinoma patients. RESULTS Patients with synchronous and metachronous breast carcinoma had worse 5‐ and 8‐year NED survival rates compared with unilateral breast carcinoma patients, as well as an increased risk of distant metastasis. In multivariate analysis, differences in local control and overall survival were not statistically significant for patients who had bilateral disease compared with those who had unilateral disease. There was no difference when patients with metachronous and unilateral breast carcinoma were compared with respect to local control and overall survival. CONCLUSIONS Patients with bilateral breast carcinoma who present with synchronous disease are at greater risk for distant metastasis than women with unilateral or metachronous breast tumors. There was a trend toward decreased overall survival and local control for patients with synchronous bilateral breast carcinoma compared with patients who had either metachronous or unilateral disease. Cancer 2000;88:2739–2750. © 2000 American Cancer Society.