It is not clear whether a healthy lifestyle affects mortality of patients with inflammatory bowel diseases (IBD), including Crohn's disease (CD) and ulcerative colitis (UC).We collected data form the Nurses' Health Study (1986-2014), Nurses' Health Study II (1991-2015), and Health Professionals Follow-up Study (1986-2014), which assess lifestyles with serial questionnaires. We estimated joint and individual associations between 5 healthy lifestyle factors after IBD diagnosis (never smoking, body mass index 18.5-24.9 kg/m2, vigorous physical activity in the highest 50% with non-zero value, alternate Mediterranean diet score 4, and light drinking [0.1-5.0 g/d]) and mortality using Cox proportional hazards models.We documented 83 deaths in 363 patients with CD during 4741 person-years and 80 deaths in 465 patients with UC during 6061 person-years. The median age of IBD diagnosis was 55 y. Compared to patients with IBD with no healthy lifestyle factors, patients with IBD with 3-5 healthy lifestyle factors had a significant reduction in all-cause mortality (hazard ratio [HR], 0.29; 95% CI, 0.16-0.52; Ptrend15 g/d 1.84; 95% CI, 1.02-3.32). The findings did not change when we adjusted for family history of IBD, immunomodulator use, and IBD-related surgery.In an analysis of data from 3 large cohort studies, we associated adherence to a healthy lifestyle with reduced mortality in patients with CD or UC.