Two hundred and fourteen patients with Crohn's disease (CD) were investigated by radiological methods, endoscopy, and histological examinations of multiple biopsy and surgical specimens. Radiological lesions suggestive of CD were found in all patients with small-bowel disease but in less than half of those with large-bowel CD. Endoscopic findings were conclusive in 36% of patients with small-bowel disease, in 91% of those with small- and large-bowel disease, and in 86% of those with CD of the large bowel. Histological examinations of biopsy specimens were conclusive in less than one third of the patients. Histological examination of operative specimens, however, was conclusive in 90-100% of all patients. In 43 patients initially diagnosed as having ulcerative colitis, abdominal pain was less frequent, but diarrhea and visible blood were more frequent as initial symptoms. Of these patients, 21 had combined small- and large-bowel disease at the end of the observation time. In intestinal CD, multiple biopsy specimens may disclose Crohn-specific lesions even in endoscopically normal mucosa at a distance from visible lesions.