The clinicopathological characteristics of breast cancer in 95 women between the ages of 24 and 45 years with a family history of breast cancer were compared with tumours from 329 women with sporadic disease matched for age and year of diagnosis. There was a trend for the family history patients to have slightly smaller tumours (mean size 2.49 cm) than the controls (mean 3.04 cm) (Mann-Whitney test, P = 0.09). A significantly greater proportion of the familial cases had grade III infiltrating ductal carcinoma than did the controls (40% vs 27%; chi2(1) = 5.64, P = 0.02). Despite this, there were more cases of operable node-negative disease among the study group than among the controls (48% vs 32%; chi2(1) = 8.2, P = 0.004). There was a highly significant survival advantage for patients with a family history (chi2 = 22.4, P < 0.001). Five- and 10-year survival rates were 92% and 87% for those with a family history compared with 70% and 54% for those in the control group. This survival advantage was maintained when patients with operable disease only were considered. In multivariate analysis, which included age, tumour size, stage, histological grade and family history, family history was an independent predictor of favourable prognosis and, in a Cox model, was associated with a relative risk of survival of 6.11 (95% CI 2.81-13.28). These results suggest that familial breast cancer has a more favourable clinical course than the more common sporadic forms of the disease.