Two infants are described with 'prune belly anomaly' (PBA) and concomitant trisomy 18. Severe abdominal distention was detected prenatally in one by ultrasonographic study, and in the second child at birth. Other chromosome abnormalities previously associated with PBA also are reviewed. The prune belly anomaly constitutes a malformation sequence that is causally nonspecific and which may occur in diverse aneuploidy syndromes. Aneuploidy is important to detect in prenatally diagnosed cases in which intrauterine fetal treatment is being considered.