Four hundred and twenty-three patients with Crohn's disease have been reviewed, 48 of whom had isolated anorectal involvement--an incidence of 11.4 per cent. These patients were compared with 48 randomly selected and sex-matched cases who presented with isolated ileocolic disease. The age of the anorectal patients (53.6 +/- 18 years) was greater than that of the controls (34.2 +/- 12 years). The duration of follow-up was 6.0 +/- 4 years and 12.6 +/- 8 years respectively. Rectal bleeding, diarrhoea and perianal disease were more common in the anorectal group. Twenty-two patients (46 per cent) with anorectal disease and 40 (83 per cent) in the ileocolic group underwent definitive surgery. There were 4 (18 per cent) postoperative deaths in the anorectal group and none among the controls. The incidence of recurrence was lower among the anorectal patients (21 per cent) compared with the ileocolic group (40 per cent). However, the estimated probability of recurrence, based on the duration of follow-up, the number of deaths during follow-up and the actual incidence of recurrence, is similar in both groups.