The accuracy of fine needle aspiration cytology has been assessed in 480 consecutive breast lesions where definitive histology was later available. The results in terms of specificity and sensitivity have also been compared to mammography and clinical examination. With adequate smears aspiration cytology was 100 per cent specific with no false positive diagnosis. This compares with 15 false positive mammograms and 12 false positive diagnoses on clinical examination. Cytology was unsatisfactory in 36 per cent of benign lesions owing to poor cellularity of the sample but when considered with mammography and examination led to a reduction in biopsies for benign disease. A definitive cytological diagnosis of malignant tumours resulted in a reduction in frozen sections with a substantial saving of resources and improvement in patient counselling. No mastectomy was performed for benign disease.