Three cases of a lethal malformation syndrome with severe visceral anomalies were seen in two families and include one pair of sibs. The predominating external manifestations are mesomelic dwarfism, micrognathia, V-shaped upper lip, microglossia, thick alveolar ridges, ambiguous genitalia, webbed neck, highly arched palate, clubfeet, fused fontanelles, inclusion cysts of the tongue, four-finger creases, digital anomalies, apparently low-set ears, widely spaced nipples, and dislocated thighs and forearms. The internal findings include oligopapillary renal hypoplasia, severe congenital heart defect, cerebellar hypoplasia, pulmonary hypoplasia, hypoplastic larynx, and hypoplastic gallbladder. Other findings from the two autopsies and one clinical investigation not documented in all three patients include unilobar lungs, hydrocephalus, cataracts, microphthalmia, polydactyly, islet cell hyperplasia, suprapubic skin crease, urethral anomalies, and a decreased number of turns of the cochlea. The hypoplasia seen in the several affected organs is similar to the disordered development seen in experimental models of branching epithelial morphogenesis in which mesenchymal-epithelial interaction has been disrupted.