We evaluated the sensitivity and specificity of Technetium-99m (99mTc)-white blood cell (WBC) for identifying terminal ileum inflammation in children with Crohn's disease (CD). In 40 children, total colonoscopy was done within a few days of a 99mTc-WBC scan carried out to evaluate the inflammation in children with CD. In 38 patients the intensity and the location of inflammation shown on the 99mTc-WBC scan of the colon were similar to the biopsy result of the colonoscopy. The sensitivity of the 99mTc-WBC scan was 97% in assessing colonic inflammation compared with colonoscopy. The 99mTc-WBC scan allowed evaluation of inflammation in the terminal ileum in 21 patients in whom the endoscopist did not cannulate the terminal ileum. Of the 19 patients in whom the terminal ileum was visualized endoscopically (14) or surgically (5), the 99mTc-WBC scan findings showed a similar degree of inflammation in 17. The 99mTc-WBC scan was abnormal in 10 of these 21 children in whom the gastroenterologist did not reach the terminal ileum. In these children with no ileoscopy the results of the 99mTc-WBC scan were consistent with the laboratory values, the gastroenterologist's clinical assessment and with long-term clinical follow-up. Finally, the 99mTc-WBC scan of 83 controls did not reveal any false-positive findings in the terminal ileum (colonoscopy result available in 30 controls). When total colonoscopy or ileoscopy is not performed or when contrast radiography is negative or unable to differentiate CD from lymphoid nodular hyperplasia, scintigraphy can demonstrate the presence of ileitis and/or colitis.