Abstract Background and Aims The development programm UNIFI has shown promising results of ustekinumab in ulcerative colitis [UC] treatment which should be confirmed in clinical practice. We aimed to evaluate the durability, effectiveness, and safety of ustekinumab in UC in real life. Methods Patients included in the prospectively maintained ENEIDA registry, who received at least one intravenous dose of ustekinumab due to active UC [Partial Mayo Score [PMS]>2], were included. Clinical activity and effectiveness were defined based on PMS. Short-term response was assessed at Week 16. Results A total of 95 patients were included. At Week 16, 53% of patients had response [including 35% of patients in remission]. In the multivariate analysis, elevated serum C-reactive protein was the only variable significantly associated with lower likelihood of achieving remission. Remission was achieved in 39% and 33% of patients at Weeks 24 and 52, respectively; 36% of patients discontinued the treatment with ustekinumab during a median follow-up of 31 weeks. The probability of maintaining ustekinumab treatment was 87% at Week 16, 63% at Week 56, and 59% at Week 72; primary failure was the main reason for ustekinumab discontinuation. No variable was associated with risk of discontinuation. Three patients reported adverse events; one of them had a fatal severe SARS-CoV-2 infection. Conclusions Ustekinumab is effective in both the short and the long term in real life, even in a highly refractory cohort. Higher inflammatory burden at baseline correlated with lower probability of achieving remission. Safety was consistent with the known profile of ustekinumab.