Over 30 cases of group 16-18 trisomy syndrome have been reported. The most common defects are summarized in the Table. Included in these defects are structures derived from all three primary germ layers. Clinically, these infants can be recognized by the abnormally shaped skull, low-set ears, micrognathia, and peculiar flexion deformities of the fingers. The following report describes an additional case of trisomy 17 and speculates upon the production of the derangements observed. Report of Case The patient was a Caucasian female born Nov 28, 1962. Labor was spontaneous and uneventful after a 37-week gestation. The placenta was reported to be very small. Examination revealed a scrawny infant weighing 3 lb 12 oz (1.7 kg) and measuring 18 inches. The head was 13 inches in circumference and was oddly shaped. The face was narrow and the jaw underdeveloped. The thorax appeared unexpanded, and there were many rales throughout both lungs.