To describe the differences in clinical characteristics and outcome between adult- and childhood-onset biopsy-proven IgA vasculitis (IgAV) in North America. Patients with IgAV diagnosed from January 1, 1997, through December 31, 2016, were retrospectively identified. Data were abstracted from direct medical record review. Kaplan-Meier methods were used to estimate survival rates. A total of 243 patients with IgAV were included (227 93.4% white, 141 58.0% male); 174 patients were adults (≥21 years), and 69 were younger than 21 years. Compared with patients younger than 21 years, adults at baseline more frequently had ulcerative skin lesions (19 10.9% vs 1 1.4%; P=.02) and nephrotic-range proteinuria (21 of 96 21.9% vs 1 of 38 2.6%; P=.007) but less commonly had abdominal pain (59 33.9% vs 42 60.9%; P<.001), ischemic gastrointestinal tract involvement (18 10.3% vs 14 20.3%; P=.04), and arthralgias (66 37.9% vs 42 60.8%; P<.001). During 389 person-years of follow-up, 29 deaths were observed. Five-year survival rates for patients aged younger than 21, 21 to 50, and 51 years or older were 100%, 94%, and 40%, respectively. In comparison to data from the United States life tables for whites, patients 51 years or older at diagnosis had a greater than 7-fold increased risk of mortality (standardized mortality, 7.60 95% CI, 5.01-11.06; P<.001). IgA vasculitis in adults is associated with more severe skin/kidney involvement and poorer renal outcome. Among adults with IgAV, patients aged 51 years or older at diagnosis have significantly higher mortality (P<.001).