Background & Aims The influence of age on the presentation, clinical course, and therapeutic response of patients with adult-onset ulcerative colitis (UC) is understudied. Given potential age-related differences in risk factors and immune function, we sought to determine if disease behavior or clinical outcomes differed between patients diagnosed with UC in later versus earlier stages of adulthood. Methods We performed a retrospective cohort study of 295 patients with UC seen at a tertiary care center from 2001 to 2008. Adult subjects newly diagnosed with UC between the ages of 18 and 30 years were defined as early onset, those newly diagnosed at age 50 or older were defined as late onset. The 2 groups were analyzed for differences in medication use and clinical end points, including disease extent, severity at the time of diagnosis, and steroid-free clinical remission at 1 year after disease onset. Results Disease extent and symptom severity were similar between groups at the time of diagnosis. One year after diagnosis, more patients in the late-onset group achieved steroid-free clinical remission (64% vs 49%; P = .01). Among those who required systemic steroid therapy, more late-onset patients achieved steroid-free remission by 1 year (50% vs 32%; P = .01). Former smoking status was a more common risk factor in the late-onset cohort ( P < .001), whereas more early onset patients had a positive family history ( P = .008). Conclusions Patients with early and late-adult-onset UC have similar initial clinical presentations, but differ in disease risk factors. Late-onset patients have better responses to therapy 1 year after diagnosis.