Background The long-term efficiacy for thiopurinic drugs in Crohn’s disease (CD), and particularly in ulcerative colitis (UC), has been insufficiently studied.

Aim To evaluate prospectively and compare the long-term effectiveness of azathioprine (AZA) in CD and UC.

Methods Three hundred and ninety-four AZA treated patients were included consecutively included. Truelove-modified index and CDAI were used to assess effectiveness. Hospitalizations and surgical procedures were recorded.

Results Two hundred and thirty-eight patients with CD and 156 with UC received AZA for a median of 38 months. Effectiveness: Partial response/remission was achieved in 34%/49% of CD patients and in 47%/42% of UC (nonstatistically significant differences). Steroid treatment: Prior to AZA, 49% of CD patients were receiving steroids, whereas only 8% needed steroids after therapy (P < 0.001). Corresponding figures in UC patients were 39% vs. 9% (P < 0.001). Hospitalizations: Prior to AZA, the rate of hospitalizations in CD was 0.190 per-patient-year, while after treatment, it decreased to 0.099 (P < 0.001). Corresponding hospitalization rates in UC were 0.108 vs. 0.038 (P < 0.001). Surgery: The rate of surgery in CD prior/after AZA was 0.038/0.011 per-patient-year (P < 0.001). The number of surgical interventions in UC prior/after AZA treatment was 26/0 (the rate per-patient-year was 0.018/0) (P < 0.001).

Conclusions Our results confirm the effectiveness of AZA in inflammatory bowel disease, not only in the short term but also in the long term, resulting in a steroid sparing effect and in both a reduction in the number of hospitalizations and surgical procedures. AZA is similarly effective for both CD and UC patients.