Background: With the extensive use of mesalamine, the natural history of ulcerative colitis is probably changed.

Objective: To evaluate the relapse rate and the duration of remission in patients with ulcerative colitis on maintenance treatment with mesalamine.

Methods: Enrolled in the study were 95 patients divided into 4 groups according to macroscopic location of the disease and treated with the same therapy starting from the date of enrolment. Patients in all 4 groups were followed-up until relapse occurred. The disease activity was evaluated by the Clinical Activity Index and Endoscopic Index. Patients suitable for recruitment showed a Clinical Activity Index and Endoscopic Index lower than 6 and 4, respectively. The patients with ulcerative pancolitis or left-sided colitis were treated with 1.6 g/day while the cases with proctosigmoiditis or proctitis were treated with 5-acetylsalicylic acid enemas 4 g/day Each patient was evaluated with clinical and endoscopic assessment at a 6-month interval. Relapse was defined as an increase in Clinical Activity Index and Endoscopic Index, of more than 6 and 4, respectively.

Results: Five patients dropped-out. All enrolled patients showed a clinical and/or endoscopic relapse within 10 years, the majority 2 or 3 years after diagnosis: pancolitis and left-sided colitis within 2-3 years and patients with distal colitis within 9-10 years.

Conclusions: A relapse was observed in most cases within 3 years, and in all recruited patients within a space of ten years. The extent of the disease in the colon is an important prognostic factor, as patients with distal colitis showed a lesser tendency to relapse.