We are unaware of any other anatomical study which deals with normal variations in the relationship between the superior mesenteric artery (SMA) and the superior mesenteric vein (SMV). In our investigation in the majority of cases, the SMV lies to the right of the SMA. It has been suggested that ultrasonographic demonstration of a left sided SMV, is characteristic of midgut malrotation so a prospective study was undertaken in order to try to correlate the position of the mesenteric vessels on Ultrasound with the radiological diagnosis of midgut malrotation on upper GI series. 427 children (95% infants) who were planned for upper GI investigation, have had color Doppler U.S. of the mesenteric vessels before the barium study. In 67 cases, the mesenteric vessels were obscured by intestinal gas. Among them, there were 2 cases of malrotation. Three different positions of the mesenteric vessels were found in the 360 remaining cases. 1) A left sided SMV was found in 4% of the cases, all had midgut malrotation on X-rays and at surgery. 2) A mesenteric vein anterior to the SMA was found in 5% of the cases, 28% had midgut malrotation. 3) A normal right sided SMV was found in 91% of the cases. However 3% of these had midgut malrotation. There are anatomical variations in the position of the mesenteric vessels and a normal relationship between SMA and SMV does not exclude the possibility of intestinal malrotation. Nevertheless, ultrasound remains a useful noninvasive screening technique for the diagnosis of midgut malrotation.