Urine cytology is a feasible tool for assessing erythematous bladder lesions after bacille Calmette-Guérin (BCG) treatment.

Bladder lesions after BCG instillations pose a challenge during follow-up and the appropriate management strategy is not clear. Lesions should not be overlooked as being BCG-induced irritation because they may harbour significant malignancies. The presence of papillary or flat tumour always warrants a biopsy or resection. In the case of erythematous lesions, our results suggest that biopsy may be avoided if voided urine cytology is negative.