A histological review of 1003 invasive breast carcinomas identified 103 patients with infiltrating lobular carcinoma, for whom clinical and survival data were collected in each case. Six patients had bilateral carcinoma at diagnosis and 14 developed a contralateral carcinoma during the period of follow-up. The major factor predicting patients at risk of developing a contralateral carcinoma was histological type. Analysis of survival data on the patients with bilateral disease showed poor survival in the group with synchronous bilateral disease, but no difference in survival between patients with metachronous bilateral and unilateral disease. This suggests that the development of a metachronous contralateral carcinoma does not necessarily reduce the probability of survival of patients with infiltrating lobular carcinoma.