The outcome and prognostic factors of 217 women with invasive lobular carcinoma (ILC) and those of 1121 women with invasive ductal carcinoma (IDC) of the breast were compared. The patients were followed up for 10-43 years. Women with ILC had axillary nodal metastases less frequently than those with IDC (43% vs 53%, P = 0.02), although there was no difference in the primary tumour size between the groups. ILCs were more frequently of low grade, had lower mitotic counts and had less tumour necrosis. Furthermore, ILCs had lower S-phase fractions and were more often DNA diploid in flow cytometric analysis than IDCs (P < 0.0001 for all comparisons). The 5- and 30-year corrected survival rates of women with ILC were 78% and 50%, respectively, compared with 63% and 37% for women with IDC (P = 0.001). Small pT1NOMO ILCs (n = 41) had 100% 10-year and 83% 20-year corrected survival rates. In a multivariate analysis, a large primary tumour size, the presence of axillary nodal metastases, a high mitotic count and the presence of tumour necrosis all had an independent prognostic value in ILC. We conclude that ILC is associated with better survival than IDC.