Monocentric observational retrospective/prospective pharmacological study. Clinical records of patients with Ulcerative Colitis and Crohn's Disease who started therapy with Ustekinumab between February 2019 and March 2021 at the IBD Unit will be reviewed. The main objective is to evaluate the overall persistence of patients with Crohn's Disease and Ulcerative Colitis who started Ustekinumab between February 2019 and March 2021, as well as the impact of treatment on the natural history of the disease. The study involves the collection of follow-up data for a maximum period of 24 months from the start of therapy. For patients who began therapy with Ustekinumab from February 2019 up to 24 months before the start of enrollment, data collection will be conducted retrospectively. For patients who have undergone therapy with Ustekinumab within 24 months prior to the start of enrollment, and up to March 2021, data will be collected both retrospectively and prospectively.