The etiology of congenital diaphragmatic hernia (CDH) is not yet known. Studies in the literature from 1941 have reported that nutritional deficiency of vitamin A during pregnancy could lead to CDH, associated or not with other malformations in young rats. More recently, possible correlations between expression patterns of cellular retinoid-binding protein and retinoic-acid receptors and morphologic effects of vitamin A deficiency have been suggested. The purpose of this study was to verify in human newborns the possible link between vitamin A deficiency and CDH previously observed in experimental animals. Blood samples were obtained during the first hours after birth from 11 term CDH newborns and 11 healthy controls matched for gestational age, and also from 7 mothers in each group, for a total of 7 newborn-mother pairs of matched CDH-controls. Plasma retinol was measured by high-performance liquid chromatography and retinol-binding protein (RBP) by nephelometry. In the 11 matched CDH-control newborns, plasma retinol and RBP levels in CDH newborns were 50% less than control values (P< 0.0002 and <0.006, respectively); in contrast, retinol levels in CDH mothers were significantly higher than those of control mothers (P < 0.005). The observation that the plasma concentrations of retinol and RBP are low in infants with CDH relative to controls may be clinically very relevant and may help to elucidate the mechanism of development of this congenital anomaly.