THE SIMULTANEOUS occurrence of two independent chromosomal anomalies in a given individual has been reported for various combinations of aberrations. Such associations most frequently involve aneuploidy of a sex chromosome and trisomy of an autosome,1-18 while double autosomal trisomies are less frequent.19-23 This report describes the second case of a patient with 48 chromosomes manifesting the cytogenetic abnormalities associated with both Klinefelter's syndrome and trisomy-18. Report of a Case The propositus was born following a 40-week gestation period and an uncomplicated delivery to a 21-year-old mother and 35-year-old father. He was the product of the mother's second pregnancy, the first resulting in a normal male. The present pregnancy was not complicated by any illness or trauma and there was no history of drug ingestion. At birth, the infant weighed 2,670 gm (5.88 lb) and was 47 cm (18.5 inches) long with a head circumference of 34 ½ cm.