We report on a severely retarded girl with multiple congenital anomalies. Chromosome studies showed a der (8) chromosome with dup(10p) and deficiency for a small distal segment of 8q. Her father proved to be carrier of a de novo balanced translocation between chromosome 8q and 10p. At 1 year the patient was also found to have the Pendred syndrome, an autosomal recessive defect in thyroid organification. The concurrence of chromosome anomalies and single gene disorders might not be too rare, but can be easily overlooked. Yet there are important consequences for genetic counseling. Moreover, recognition of these concurrences may help gene mapping.