Since 1970 fine-needle aspiration cytology for breast tumours has grown in popularity and is now routinely used in the initial diagnosis of palpable breast masses in the United States and other parts of the world. Fast staining methods of the aspirate enables reporting within 10 minutes of the aspirate being performed. Training and experience is important in obtaining satisfactory smears for diagnosis, and pitfalls are false-negative and false-positive findings, which may have dire consequences for the patient if cytological diagnosis is the final arbiter. Conditions such as benign mammary dysplasia and sclerosing adenosis are the most common sources of highly cellular smears and often show marked atypia, which makes distinction from carcinoma difficult. Also, atypical papillary formations present a diagnostic problem, and biopsy is indicated to exclude a papillary carcinoma. Fine-needle aspirations very seldom cause traumatic complications, and these are usually of a minor degree. Seeding along the needle track has occurred, but in most cases with a larger-caliber (18 s.e.g.) needle. Aspiration itself has been shown to have no effect on the survival rates in breast carcinoma. Contemporary reports show that around 90% of cases of breast cancer can be detected with confidence by means of this procedure. The reduction in scar formation facilitates future evaluation of the patient as scar tissue often interferes with the interpretation of mammograms. Cost effectiveness is evident in terms of decreased use of anaesthetics and operating time and a reduction in the use of frozen section histology by about 80%.(ABSTRACT TRUNCATED AT 250 WORDS)