Clinical observations and autopsy findings in 16 cases of full 18 trisomy are presented. These patients were seen during the ten-year period of 1971-1981. In 14 cases, typical clinical features allowed a tentative diagnosis. However, two cases presented with an atypical phenotype: a Potter's syndrome associated with urethral atresia was superimposed, obscuring the more classical trisomy 18 stigmata. This combination is believed to be unique. Cardiovascular defects, varying in type and degree were invariably present. A very high incidence of major gastrointestinal and urogenital abnormalities was also noted. Histological abnormalities giving evidence of organ dysplasia, were observed in the central nervous system, pancreas, kidneys and ovaries.