Primary malignant melanoma of the urinary bladder.

A melanin-synthesizing tumor of the urinary bladder was studied by light and electron microscopy. Careful clinical evaluation did not reveal evidence for a primary melanoma elsewhere in the patient. The clinical presentation, course of the disease, and demonstration of melanocytes in the bladder epithelium and malignant melanocytes comprising the tumor by light and electron microscopy indicated that the neoplasm was a primary malignant melanoma arising in the bladder.