Background: The incidence of inflammatory bowel disease (IBD) is increasing worldwide.

Objective: To evaluate the incidence of IBD in Castilla y León describing clinical characteristics of the patients at diagnosis, the type of treatment received and their clinical course during the first year.

Methods: Prospective, multicenter and population-based incidence cohort study. Patients aged >18 years diagnosed during 2017 with IBD (Crohn's disease [CD], ulcerative colitis [UC] and indeterminate colitis [IC]) were included from 8 hospitals in Castilla y León. Epidemiological, clinical, and therapeutic variables were registered. The global incidence and disease incidence were calculated.

Results: 290 patients were diagnosed with IBD (54.5% UC, 45.2% CD, and 0.3% IC), with a median follow-up of 9 months (range 8-11). The incidence rate of IBD in Castilla y Leon in 2017 was 16.6 cases per 10,000 inhabitants-year (9/105 UC cases and 7.5/105 CD cases), with a UC/CD ratio of 1.2:1. Use of systemic corticosteroids (47% vs 30%; P=.002), immunomodulatory therapy (81% vs 19%; P=.000), biological therapy (29% vs 8%; P=.000), and surgery (11% vs 2%; p=.000) were significatively higher among patients with CD comparing with those with UC.

Conclusions: The incidence of patients with UC in our population increases while the incidence of patients with CD remains stable. Patients with CD present a worse natural history of the disease (use of corticosteroids, immunomodulatory therapy, biological therapy and surgery) compared to patients with UC in the first year of follow-up.