The radiographic manifestations of Down's syndrome have been described by many authors. Recently, several new stigmata have been published (3–5). The pelvic characteristics in this syndrome, as described by Caffey and Ross (1, 2), remain the most constant radiologic abnormalities; but in a small percentage of infants the pelvis is normal. The roentgen diagnosis of mongolism, therefore, must be substantiated by other findings, and finally by chromosomal analysis. The purpose of this paper is to present a new radiologic finding and to show its relatively high incidence in this chromosomal abnormality. Figure 1 is the chest radiograph of a newborn girl first seen because of duodenal atresia. Although the infant was clinically mongoloid, the pelvic radiograph disclosed normal iliac and acetabular contours. However, accessory sternal ossification centers (4) and congenital heart disease were present. In addition, only 11 pairs of ribs were counted. Genetic studies revealed a trisomy of the No. 21 chromosome. B...