BACKGROUND Primary melanoma of the urinary bladder is a rare neoplasm, and there have been no prior reports in which the initial diagnosis was made by urinary cytology. METHODS An 82-year-old woman presented with vaginal spotting, gross hematuria and dysuria. Voided urine cytology revealed malignant cells, several of which exhibited cytoplasmic melanin pigment and were accompanied by many macrophages also containing melanin. Cystoscopy revealed a darkly pigmented, polypoid mass at the bladder neck. Biopsy confirmed the diagnosis. CONCLUSIONS Primary melanoma of the urinary bladder is rare. The diagnosis can be made on cytologic examination of voided urine if careful study of exfoliated malignant cells reveals cytoplasmic melanin pigment. Macrophages may also harbor melanin pigment, and their presence should alert the cytopathologist to search carefully for pigmented malignant cells. Clinical and radiologic studies are essential to rule out melanoma metastatic to the bladder.