The histological tumour type determined by current criteria has been investigated in a consecutive series of 1621 women with primary operable breast carcinoma, presenting between 1973 and 1987. All women underwent definitive surgery with node biopsy and none received adjuvant systemic therapy. Special types, tubular, invasive cribriform and mucinous, with a very favourable prognosis can be identified. A common type of tumour recognized by our group and designated tubular mixed carcinoma is shown to be prognostically distinct from carcinomas of no special type; it has a characteristic histological appearance and is the third most common type in this series. Analysis of subtypes of lobular carcinoma confirms differing prognoses. The classical, tubulo-lobular and lobular mixed types are associated with a better prognosis than carcinomas of no special type; this is not so for the solid variant. Tubulo-lobular carcinoma in particular has an extremely good prognosis similar to tumours included in the 'special type' category above. Neither medullary carcinoma nor atypical medullary carcinoma are found to carry a survival advantage over carcinomas of no special type. The results confirm that histological typing of human breast carcinoma can provide useful prognostic information.