Sixty-five consecutive patients seen in a pediatric emergency department, in whom the diagnosis of intussusception was considered, had an ultrasound examination of the abdomen before a barium enema. The mean age of the patients was 1.7 years (range 2 weeks to 5 years). Intussusception was detected by ultrasonography in all 20 cases proved by barium enema. There were three false-positive ultrasound results (sensitivity = 100%, confidence interval (Cl) = 86% to 100%; specificity = 93%, Cl = 86% to 96%). Normal findings on ultrasonography correlated with a negative barium enema results in 42 of 42 cases (negative predictive value = 100%, Cl = 94% to 100%). No intussusception was missed by ultrasonography. To determine which patients would most benefit from ultrasonography, we divided patients into either a high-risk group (81% with intussusception) or a low-risk group (14% with intussusception) on the basis of clinical symptoms (p less than 0.01). If each high-risk child had a barium enema and each low-risk child had an ultrasound study as their initial diagnostic test, 89% of the patients in this study would have undergone only one examination. We conclude that ultrasonography can be used as a rapid, sensitive screening procedure in the diagnosis or exclusion of childhood intussusception. Children considered at low risk of having intussusception on the basis of clinical symptoms should initially have an ultrasound examination; patients at high risk should have an immediate barium enema.