AbstractThe monoclonal antibody (MAb) Ki67 detects a nuclear antigen in cycling tumor cells. Quantitation of proliferating cells is helpful in predicting the recurrence and metastatic potential of tumors as previously reported. We conducted a prospective study on 40 benign and malignant tumors by performing Ki67 immunocytochemical stains on cytologic smears and their corresponding frozen tissues. Quantitation of Ki67 positive cells was done by counting 300 cells in 5‐7 high‐power fields in cytologic smears and tissues. Only nuclear or nucleolar immunostaining was considered positive for MAb Ki67. The number of Ki67 positive tumor cells in cytologic smears correlated well with Ki67 positive cells from corresponding tissues. On the average, cytologic smears showed 1.9% higher Ki67 positivity in malignant tumors as compared to their corresponding frozen tissues (P<0.001). The Ki67 positivity in malignant tumors was found to be significantly higher when compared with benign tumors (P<0.001). We conclude that cytologic smears can be used for the determination of growth potential in tumors by MAb Ki67. Additionally, cytologic preparations can be used during intraoperative consultations when adequate tissue is not available for the above mentioned st