OBJECTIVE: To compare differences in long-term outcome between adults with childhood-onset (age at diagnosis <18 years) systemic lupus erythematosus (SLE) and with adult-onset SLE. METHODS: Data were derived from the University of California Lupus Outcomes Study, a longitudinal cohort of 885 adult subjects with SLE (90 childhood-onset [cSLE], 795 adult-onset [aSLE]). Baseline and 1-year followup data were obtained via structured 1-hour telephone interviews conducted between 2002 and 2006. Using self-report data, differences in organ involvement and disease morbidity, current disease status and activity, past and current medication use, and number of physician visits were compared, based on age at diagnosis of SLE. RESULTS: Average disease duration for the cSLE and aSLE subgroups was 16.5 and 13.4 years, respectively, and mean age at followup was 30.5 and 49.9 years, respectively. When compared with aSLE subjects, cSLE subjects had a higher frequency of SLE-related renal disease, whereas aSLE subjects were more likely to report a history of pulmonary disease. Rates of clotting disorders, seizures, and myocardial infarction were similar between the 2 groups. At followup, cSLE subjects had lower overall disease activity, but were more likely to be taking steroids and other immunosuppressive therapies. The total number of yearly physician visits was similar between the 2 groups, although cSLE subjects had a higher number of nephrology visits. CONCLUSION: This study demonstrates important differences in the outcomes of patients with cSLE and aSLE, and provides important prognostic information about long-term SLE disease activity and treatment.