A fatal case of the megacystis-microcolon syndrome in a newborn girl is presented and two previously unreported findings are discussed. The umbilical hernia is thought to represent a mechanically induced embryological defect, secondary to the expanding nonfunctional megacystis which appears to be the dominant component from an early stage. Hypertrophic changes of the large intestinal wall musculature, adjacent to dilated segments, may indicate an impaired propulsive activity in utero, as a result of defective neurotransmission. The latter is proposed as the common pathophysiological mechanism for both urinary and intestinal malfunction.