To compare the 6-month efficacy and tolerance of azathioprine in 68 patients with steroid-resistant or steroid-dependent chronic ulcerative colitis (n = 30) or Crohn's disease (n = 38).

Clinical remission was defined as a Crohn's Disease Activity Index < 150 for Crohn's disease and number of non-bloody stools <= 3/day for ulcerative colitis, associated with prednisone requirement <= 10 mg/day.

Seventy-three per cent of patients with ulcerative colitis had distal or left-sided colitis and 84% of patients with Crohn's disease had pancolitis. Azathioprine was discontinued early for side-effect in 8 (26.7%) patients with ulcerative colitis and in 8 (21.1%) patients with Crohn's disease (NS). In patients treated at least 6 months by azathioprine, clinical remission rates were 77.3% and 70% for chronic ulcerative colitis and Crohn's disease (NS). Complete corticosteroids weaning was obtained significantly more often in ulcerative colitis patients than in Crohn's disease patients (59.1% vs 30 %; P < 0.05).

Azathioprine seems to be at least as effective and equally tolerated in steroid-resistant or steroid-dependent chronic ulcerative colitis or Crohn's disease patients.