The histology and clinical records of 52 patients with bilateral breast cancer recorded in a community tumor registry were reviewed. Previous studies have demonstrated the propensity of lobular carcinoma to occur bilaterally. This view is supported by the large number of lobular cancers found in our patients. Thirty-six percent of the patients with bilateral disease had lobular cancer in at least one breast. Those with lobular cancer tended to be younger and more likely to have simultaneous cancers than did patients with nonlobular carcinoma. In those patients in whom the occurrence of tumors was not simultaneous, they were smaller in the second breast but had similar rates of axillary metastases. This study raises the question of how best to manage the contralateral breast in patients with breast cancer. Lobular carcinoma is one marker of the likelihood for development of disease in the second breast; but if advantage is to be gained by this finding, investigation of the opposite breast is best done early. Finally, thorough examination of patients with nonlobular carcinoma must not be ignored because they still comprise the majority of bilateral breast cancers.