OBJECTIVE: The advent of biological drugs has revolutionised management of inflammatory bowel disease (IBD). However, the extent to which these novel pharmacological drugs have reduced the need for surgical treatment remains incompletely quantified.We aimed to investigate the risk of first, major surgery in IBD in a population-based, large epidemiological study. METHODS: We empanelled a cohort comprising all 85 974 patients diagnosed with ulcerative colitis (UC) and 42 760 with Crohn's disease (CD) in Norway and Sweden in 1987 through 2017. We used log-rank tests to compare the cumulative probability of surgical treatment for UC and CD. Using multivariable Cox proportional hazards models, we estimated hazard ratios (HR) with 95% CIs by year of diagnosis, age, sex and extent of disease. RESULTS: During a mean follow-up of 9.9 years, surgery was undertaken in 11 187 (13.0%) patients with UC (12.3 per 1000 person-years) and in 11 307 (26.4%) patients with CD (30.0 per 1000 person-years). In UC, the cumulative 5-year probability of surgery decreased from 16.2% in patients diagnosed in 1987-1994 to 5.8% in those diagnosed in 2011-2017 (p<0.001). In CD, the corresponding decline was from 30.1% to 13.9% (p<0.001). In multivariable analyses, the likelihood of surgical treatment decreased during the study period by 61% (HR 0.39, 95% CI 0.36 to 0.42) in UC and by 31% (HR 0.69, 95% CI 0.65 to 0.75) in CD. CONCLUSIONS: Following the introduction of biologic drugs, the need for surgical treatments has been dramatically reduced in patients with UC and moderately reduced in patients with CD.