A child with colitis was treated for Crohn's disease, diagnosed on history, clinical and colonoscopic findings, radiolabelled white cell bowel scan, and colonic histology. After septicaemia caused by an unusual organism, further investigation lead to a diagnosis of chronic granulomatous disease (CGD). The granulomatous colitis of CGD is clinically, histologically, and on white cell scanning, indistinguishable from that in Crohn's disease and should be considered in atypical cases. Infection with unusual 'pseudomonads' should prompt the exclusion of this disorder.