Silver staining Nucleolar organizer regions (AgNORs) were studied in fine needle aspirates of 48 benign and 36 malignant lesions and correlations with histological types, menstrual status, tumor size and lymph node involvement were looked for. A semiquantitative scoring system (AgNOR Score) reflecting total AgNOR area was applied to each of these parameters and compared with the standard counting method. The objectives were to examine the pattern of distribution and discriminating capacity of AgNORs in fine needle aspirates of different breast lesions and to evaluate the AgNOR scoring system as an alternative to the standard counting method. Mean AgNOR count was significantly higher in malignant (5.4; 95% CI 5.0-5.9) than benign (2.8; 95% CI 2.7-3.0) lesions. For AgNOR scores the corresponding values were: malignant 11. 2; 95% CI 10.2-12.2 and benign 5.3;95% CI 4.9-5.7. For malignant lesions, the counts and scores tend to be more in ductal carcinomas than lobular, more in premenopausal women, in tumors more than 5 cm in diameter and in cases with more than 3 lymph nodes involved. For all parameters the scoring system showed better discriminating capacity. The differences in AgNOR scores were statistically significant for tumor size and lymph node status. Multiple stepwise regression shown tumor size to be best correlated with AgNORs.