Fine needle aspiration biopsy in the diagnosis and management of fibroadenoma of the breast. Cytological and histological biopsies were obtained on 75 breast lumps clinically diagnosed as fibroadenomas. Of these, 95 per cent of lesions were benign. In 51 (68 per cent) confirmed as fibroadenomas histologically, cytology was benign in 78 per cent, but inadequate for diagnosis in 16 per cent. The remaining 24 lesions included three breast cancers and one lymph node with Hodgkin's disease. In this group cytology was inadequate for diagnosis in 54 per cent, including one breast cancer. No lesion with benign cytology was subsequently shown to be malignant. The study supports the view that clinical diagnosis and cytology are accurate in the diagnosis of benign breast disease of this type. Breast cancer may rarely present with the clinical features of a fibroadenoma and too few lesions have been studied to assess fully the performance of cytological biopsy in detecting these small mobile lesions. A non-excisional policy should therefore include prolonged follow-up and repeat biopsy. 