Although the incidence of inflammatory bowel disease IBD is increasing in Asia, data on long-term epidemiological trends are limited. We performed a 30-year longitudinal study to investigate temporal trends in the epidemiology of Crohn's disease CD and ulcerative colitis UC in Seoul, Korea. This population-based study included 1431 IBD patients 418 CD, 1013 UC diagnosed between 1986 and 2015 in the Songpa-Kangdong district of Seoul, Korea. Temporal trends in incidence, prevalence, and disease phenotype at diagnosis were analysed. The adjusted mean annual incidence rates of CD and UC per 100 000 inhabitants increased from 0.06 (95% confidence interval CI, 0.05-0.07) and 0.29 95% CI, 0.27-0.31, respectively, in 1986-1990 to 2.44 95% CI, 2.38-2.50 and 5.82 95% CI, 5.73-5.92, respectively, in 2011-2015. Average annual percentage change in IBD incidence was 12.3% in 1986-1995, 12.3% in 1996-2005, and 3.3% in 2006-2015. The male-to-female ratio of the adjusted incidence rate was 3.3:1 for CD and 1.2:1 for UC. Perianal fistula/abscess was present in 43.3% of patients before or at CD diagnosis. At diagnosis, 54.3% of UC patients presented only with proctitis. The adjusted prevalence rate in 2015 was 31.59/100 000 95% CI, 31.10-32.07 for CD and 76.66/100 000 95% CI, 75.91-77.42 for UC. The incidence and prevalence of IBD in Korea have continued to increase over the past three decades. Korean patients have distinct demographic and phenotypic characteristics, including a male predominance and high frequency of perianal fistula/abscess in CD and high proportion of proctitis in UC.