The incidence of VEO-IBD ranged from 0.8 to 3.3/100,000/year. The mean rate of increase was 4% per year (p=0.06; CI 0%, 8%). The rate of increase was significant in males (p= 0.04) compared to females (p=0.281). The incidence of UC increased strikingly from 0.6 to 2.3/100,000/year (CI 0.025, 0.164) at an average annual rate of 9%. Pancolonic UC increased 7-fold from 0.3 to 2.3/100,000/year (p=0.005). Using PUCAI scores, severe disease activity at presentation increased significantly from 0% to 36% (p=0.002). The incidence of CD increased at a slower rate of 0.02/100,000/year (CI -0.41, 0.079). Significantly more males (44%) than females (18%) had both upper and lower GI tract involvement (p=0.03). 76% of patients with CD had inflammatory disease behaviour while 24% had stricturing or penetrating disease. A total of 31% of children presented with perianal disease. At one year follow up 64% were in clinical remission, with 56% in steroid-free remission. Fifty two (35%) children commenced immunomodulators within 1 year of diagnosis while 6 (4%) underwent surgery. At maximum follow up (median 60 months), 24 (16%) children had commenced biologics, 76 (48%) immunomodulators and 20 (13%) had undergone surgery (12 UC; 8 CD). This is the first national population-based study describing the epidemiology and outcomes of VEO-IBD phenotypes. Boys hadmore extensive disease than girls. Substantial and sustained increases in the incidence and severity of UC in particular were observed. Prospective longitudinal studies are required to fully elucidate the factors underlying the aetiology and outcome of VEO-IBD.