Of the 4,554 patients who registered at The University of Texas M. D. Anderson Cancer Center, Houston, Texas from 1965 to 1988 with a diagnosis of carcinoma of the breast and who underwent surgical treatment of at least one carcinoma of the breast at this institution, 142 had either a history of a prior carcinoma of the breast (metachronous; n = 55) or a contralateral carcinoma of the breast detected within four months of registration (synchronous; n = 87). We retrospectively studied the records of these 142 patients and found that the occurrence of bilateral carcinoma of the breast was low (3.1 percent), the frequency of metachronous carcinoma of the breast remained relatively constant over time, the nodal status of the second carcinoma of the breast correlated with the method of discovery rather than the stage of the first carcinoma of the breast and survival rates from the second carcinoma of the breast were similar for metachronous and synchronous disease. These data support the role of vigilant surveillance of the contralateral breast with screening at the time of initial diagnosis and during follow-up evaluation. Because the likelihood of detecting a second carcinoma of the breast at an early stage is high, with subsequent good survival rates, the use of prophylactic mastectomy should be very selective and based on the emotional needs of the patient.