A kindred contained at least 18 members with visceral myopathy. Sixteen had symptoms of chronic obstruction of the gastrointestinal or urinary tracts. Of six patients with megaduodenum on contrast roentgenograms, two were asymptomatic. Four patients had redundant colon on barium enema, and four had megacystis. Specimens from duodenum, jejunum, ileum, colon, or urinary bladder from five patients showed thinning and extensive collagen replacement of the longitudinal muscle layer; ganglion cells were normal by light and electron microscopy. Esophageal manometry in three patients showed decreased gastroesophageal sphincter pressures and no contractions in the smooth muscle segment of the esophagus; duodenal manometry showed a low frequency and amplitude of contractions. Three patients developed fever and signs of peritonitis after operations to bypass dilated segments. This seems to be a generalized smooth muscle disease with variable clinical manifestations and with an autosomal dominant or sex-linked dominant mode of inheritance.