A retrospective analysis was made of jejunal biopsies performed on 62 patients with Crohn's disease for disaccharidase levels and routine histology. Thirteen patients with irritable bowel syndrome acted as a control group. Two patients with Crohn's disease had hypolactasia. Two patients had marginally low sucrase levels, but all patients had normal maltase levels. Only one patient with irritable bowel syndrome had hypolactasia with normal histology. There were no significant differences between the two groups. Four patients with Crohn's disease had abnormal jejunal histology. The prevalence of hypolactasia in patients with Crohn's disease is not increased. Ideally lactase deficiency in patients with Crohn's disease should be confirmed before starting a lactose-free diet which can produce further restrictions on dietary intake.