A proband girl was investigated because of a congenital heart defect and hexadactyly. Her brother and sister died in early infancy from cardiac malformations. In the patient, satellites were found on a chromosome No. 17 in 34% of cultured lymphocytes. The same cytological anomaly was discovered in the karyotype of her normal father. In addition, this man possessed a Y chromosome with satellites at the end of the long arm. The same satellited Y was demonstrated in the paternal grandfather and the abnormal No. 17 in the paternal grandmother. The satellited Y chromosome was found associated with group D and G chromosomes in over 30% of the metaphases in both men, strongly indicating a true nucleolar-organizing region and, therefore, a translocation from an autosome. Only a few associations were noted for the abnormal No. 17, where the appearance of satellites is probably due to a secondary constriction of a different nature. The identification of the two abnormal chromosomes was confirmed by autoradiography. A direct pathogenic significance of these structural anomalies is questionable.