A 26-year-old Thai woman who has lived in Hong Kong for the past 3 years presented with a 2-month history of feverishness, intermittent epigastric discomfort, anorexia, and weight loss. She had had per rectal bleeding for 10 days. Colonoscopy on two separate occasions revealed multiple ulcerations involving the entire colon, with rectal sparing. Histological examination of the two sets of colonic biopsies that were obtained during colonoscopy suggested Crohn's disease. There was no response to mesalazine and metronidazole, but the patient responded promptly to a therapeutic trial of antituberculous drugs. Cultures from the first set of colonic biopsies were negative for acid-fast bacilli, but 8 weeks after the second colonoscopy, cultures from the second set of biopsies yielded Mycobacterium tuberculosis. This case illustrates that the diagnosis of colonic tuberculosis requires a high index of suspicion. In cases where the information available does not reveal a definite differentiation between colonic tuberculosis and Crohn's disease, corticosteroids should be withheld. The administration of corticosteroids to a patient with colonic tuberculosis may have disastrous results, and a therapeutic trial of antituberculous drugs should be considered instead.