Trisomy C is documented in a 17-hour-old full-term male infant with bilateral diffuse renal dysplasia, Potter facies, pulmonary hypoplasia and other congenital anomalies. In addition to renal dysplasia, intrahepatic bile duct and pancreatic dysplasia are demonstrated microscopically. The extra C-group autosome is morphologically consistent with a No. 11 and this is regarded as the etiology of the multiple malformations of this infant. The phenotype and the renal malformation are essentially similar to those described by Juberg et al (3) in an infant with trisomy C. It is suggested that the same chromosome is involved in both cases. Karyotype analysis should be performed on patients suspected of congenital renal malformations since the evidence implicates trisomy C as the etiology of at least some cases of bilateral renal dysplasia.