A scoring system for the assessment of fine needle aspirates of benign and malignant breast lesions was devised which showed a positive correlation (r = 0.67) between the scores obtained from the fine needle aspirates from ductal carcinomas and the Bloom and Richardson-type scores for their paired excision biopsy specimens. This system permitted grades II and III ductal breast carcinoma to be distinguished reliably from grade I tumours but no correlation with the lymph node state of patients with breast carcinoma was shown. Some overlap between the scores for grade I ductal carcinomas and some benign lesions was found, and this underlines a need for caution in the reporting of such equivocal aspirates. No cytological features that distinguished reliably ductal from lobular carcinoma were identified but the same spectrum of severity of cytological abnormality in the ductal and lobular carcinoma aspirates was seen. This system may be of prognostic value in the assessment of lobular carcinoma which has hitherto defied histological grading.