The conventional radiological techniques for the diagnosis of malrotation are prone to widely varying interpretation and may be both hazardous and impractical in the seriously ill infant. The superior mesenteric vein normally lies on the right ventral aspect of the artery, but is found on the left side in malrotation; this change in orientation can be demonstrated by ultrasound, which can provide a rapid and less invasive indication of midgut malrotation. In 19 of 39 patients with suspected malrotation, an abnormal mesenteric axis was demonstrated, and in each case the diagnosis was confirmed at surgery. Of the 20 children in whom malrotation was refuted by ultrasound, normal rotation was supported by oral contrast studies in 14 and an alternative diagnosis established in 6. A further 20 patients were scanned as a control group, and all were found to have normal vascular anatomy. This study supports the hypothesis that as a sensitive and specific investigation for midgut malrotation, the ultrasonographic appearance of the orientation of the superior mesenteric vessels is a safe and non-invasive alternative to conventional contrast studies.