BACKGROUND AND AIM: Ustekinumab is a monoclonal antibody that targets interleukin-12/23. In Scotland, it was approved for the treatment of moderate to severe Crohn's disease in 2017. The objective of this study was to establish the real-world effectiveness and safety of ustekinumab in the treatment of Crohn's disease. METHODS: We conducted a retrospective study of patients receiving ustekinumab across eight Scottish National Health Service health boards between 2017 and 2019. Inclusion criteria included a diagnosis of Crohn's disease with symptoms attributed to active disease plus objective signs of inflammation at baseline (C-reactive protein ≥ 5 mg/L or fecal calprotectin ≥ 250 μg/g or inflammation on endoscopy/magnetic resonance imaging) and completion of induction plus at least one clinical follow-up at 8 weeks. Kaplan-Meier survival analysis was used to establish 12-month cumulative rates of clinical remission, mucosal healing, deep remission, and perianal fistula response. Rates of serious adverse events were described quantitatively. RESULTS: Our cohort consisted of 216 patients (female sex, 37.9%; median age, 39.0 years, interquartile range [IQR] 28.8-51.8 years; disease duration, 9.9 years, IQR 6.0-16.5 years; prior biologic, 98.6%) with a median follow-up of 35.0 weeks (IQR 17.4-52.0 weeks). Twelve-month cumulative rates of clinical remission, mucosal healing, and deep remission (clinical remission plus mucosal healing) were 32.0%, 32.7%, and 19.3%, respectively. In patients with active perianal disease (n = 37), the 12-month cumulative perianal response rate was 53.1%. The serious adverse event rate was 13.6 per 100 patient-years of follow-up. CONCLUSION: Ustekinumab is a safe and effective treatment for the treatment of complex Crohn's disease.