OBJECTIVETo evaluate the role of micronuclei (MN) scoring in urinary cytology of bladder transitional cell carcinoma (TCC).STUDY DESIGNEighty cases of freshly voided urine samples were used for scoring of MN using acridine orange (AO)-stained smears under fluorescence microscope and routine Papanicolaou-stained smears under light microscopy. MN score for cytologic lesions was compared.RESULTSIn AO-stained slides, the mean MN scores were 0.171 +/- 0.395 and 1.489 +/- 1.871 in smears with "no malignant cells seen" and TCC cases, respectively. In Papanicolaou-stained slides the mean MN scores were 0.194 +/- 0.419 and 1.84 +/- 1.876 in smears with "no malignant cells seen," and TCC cases, respectively. Independent sample t test showed significant difference of MN scoring in Papanicolaou-stain and AO stain in no malignancy vs. TCC. Pearson's correlation test showed strong positive correlation between mean MN score by AO and Papanicolaou stains and Pearson's correlation coefficient.CONCLUSIONMN score was significantly high in TCC cases, which may be due to chromosomal damage in bladder carcinoma. In difficult cases, MN may help distinguish benign from malignant cells in urine samples. Routine Papanicolaou stain may also be used for MN score because DNA-specific AO-stained smear gives almost similar results.