PURPOSE: A grading system based on cytology would be helpful in the selection of patients for appropriate therapy. The aim of this study was to devise such a system for grading breast carcinoma based on cytological features alone. MATERIALS AND METHODS: Diagnostic fine needle aspiration (FNA) smears taken from 100 patients with invasive breast carcinoma were studied without knowledge of the subsequent grade and type of the tumors. The technique of aspiration employed a 10 ml syringe and 23 gauge needle. The aspirates were spread onto slides and half of the smears were rapidly air-dried and stained by May-Grunwald-Giemsa, while the rest were alcohol-fixed and stained by Papanicolaou technique. The features assessed were: nuclear pleomorphism, nucleoli, mitoses, nuclear/cytoplasmic ratio, apoptosis, necrosis, cell clustering, cel-lularity and tubular formation. Cytological features were compared to the histological grade of breast carcinomas following excision, and the results were analyzed by the x(2) test (the significance level was set to p<0.05), as well as by the correlation coefficients (ri). Multivariate analysis was carried out by multiple correlation coefficients (Rij) for each pair of significant parameters. RESULTS: Significant association between worsening cytological features and increasing histological grade were found with nuclear pleomorphism, nucleoli, mitoses, apoptosis, cellularity and tubular formation. A scoring system based on these 6 parameters enabled the classification of tumors into low and high cytological grades which showed a close correlation with histological grade with 81% concordance. The best multiple correlations were found for the following pairs of cytological parameters: mitoses-apoptosis (0.603), mitoses-tubular formation (0.572), apoptosis-nuclear pleomorphism (0.550) and mitoses-nuclear pleomorphism (0.545). CONCLUSION: On the basis of this study we conclude that the proposed system of grading breast carcinoma is possible from FNA cytology and it shows a good correlation with histological grade.