Of 10 patients with familial or nonfamilial visceral myopathy studied for urological manifestations only 3 had symptoms of urinary retention. Excretory urography revealed megacystis in all 3 symptomatic patients, while the 7 asymptomatic patients had normal-sized bladders. Cystometrograms performed in 4 asymptomatic patients also were normal. Bladder tissue from 5 patients was studied. Of 3 autopsy cystectomy specimens 2 were dilated severely and thin-walled without trabeculations or diverticula suggestive of mechanical obstruction. Microscopic sections showed segmental intrafascicular fibrosis in 4 patients, which was associated with elastosis in 3. Electron microscopy of leiomyocytes in abnormal fascicles revealed myofilament disorganization, lipid accumulation and increased numbers of cytoplasmic organelles. We conclude that pathological changes in the bladder occur commonly but urinary symptoms occur in less than half of the patients with visceral myopathy available for study. An abnormal excretory urogram was seen in only patients who had symptoms suggestive of lower urinary tract dysfunction.