Fine needle aspiration (FNA) cytology carried out on 1318 primary breast cancers from 1980 to 1986 inclusive showed that 198 were well recognised, histological special types. These included medullary, mucoid, tubular, cribriform and lobular invasive cancers, and non-invasive cancers. Excluding these special histological types, the overall number successfully identified (malignant plus suspicious) by fine needle aspiration was 940 (84%), although in only 820 (73%) was malignancy definitely diagnosed. The results for the special types were variable, the mucoid and medullary cancers being consistently identified while the other types were not. For tubular and cribriform, lobular and non-invasive ductal cancers a malignant diagnosis was made in 30% to 40% of cases, although inclusion of suspicious results gave identification figures of 60% to 70%. Particular cytological patterns are characteristic of some special histological cancer types but lesion cellularity, size, and physical definition are all intrinsic factors influencing success of FNA diagnosis. About 10% of all primary breast cancers seem to have certain histological properties which further reduce the success of fine needle aspiration.