In April 1960, Patau and others described a characteristic pattern of numerous anomalies associated with a trisomy in the 13–15 group (also known as D1 trisomy) (13). Although there have been over thirty published examples of trisomy 13–15, only brief mention of the disorder has been made in the radiological literature (1). After review of the radiographic features in our eight cases of trisomy 13–15, we felt that the pattern of radiologic abnormalities was diagnostic and could be differentiated from trisomy 18, cri du chat syndrome, and mongolism. Karyotype Patients with trisomy 13–15 have a basic number of 47 chromosomes with an extra chromosome in the medium-sized group (D, 13–15) that has the centromere toward one end (acrocentric) (2, 7) (Fig. 1). Trisomy 13–15 is generally thought to result from maternal nondisjunction (3, 6, 10). The similar clinical pattern of this trisomy suggests that the same genes on the same chromosomes are present in triplicate (5). Embryology The extra chromosome in the 13–...