In a retrospective review of 2820 patients with breast carcinoma seen at the Combined Breast Clinic of St George's Hospital over a 23-year period 101 cases were bilateral of which 52 (1.8%) presented synchronously and 49 (1.7%) metachronously. Twenty deaths occurred in the synchronous group after a mean follow-up of 56.2 months and 15 deaths in the metachronous group after a mean follow-up of 48.5 months following diagnosis of the second tumour. If timed from initial presentation patients with metachronous tumours fared better than those with unilateral disease (P < 0.01). There was no significant difference in survival between patients with metachronous (if timed from the second tumour), synchronous or unilateral breast carcinoma.