Aim of the study was to evaluate [99mTc]hexamethyl-propylamine-oxime (HMPAO) leukocyte scintigraphy for the assessment of disease activity and extent in inflammatory bowel disease patients. Results and scores of scintigraphy using [99mTc]HMPAO-labeled leukocytes were retrospectively compared with the activity index of van Hees, laboratory parameters, and gastroenterologists' assessment of disease using endoscopy, radiology, and histology plus clinical parameters in 136 patients with Crohn's disease (115) and ulcerative colitis (21) and in 29 controls. There were 114 positive and 22 negative [99mTc]HMPAO leukocyte scintigrams. Sensitivities for active disease at 1 and 3 hr were 98% and 98% and specificities were 100% and 83%, respectively. [99mTC]HMPAO leukocyte scintigraphy is superior to the activity index and the gastroenterologists' clinical assessment of active inflammation in IBD patients. Scintigraphy allows assessment of the existence, extent, and intensity of active inflammation in IBD patients in one examination with high accuracy.