To compare the long-term outcome in individuals with early-onset (before age 18) and adult-onset schizophrenia spectrum disorder who were initially diagnosed and treated in the same clinical center. Method: A prospective follow-up study of 723 consecutive first-episode psychosis patients (age range 14 to 30. years) on average 7.4. years after initial presentation to an early psychosis service, the Early Psychosis Prevention and Intervention Centre in Melbourne, Australia. The outcome measures included the Brief Psychiatric Rating Scale, the Schedule for the Assessment of Negative Symptoms, the Beck Depression Inventory, the Global Assessment of Functioning Scale, the Social and Occupational Functioning Assessment Scale, and the Quality of Life Scale. Results: Follow-up interviews were conducted on 66.9% (484/723) individuals, of whom 75.6% (366/484) received a schizophrenia spectrum disorder diagnosis at baseline. Early-onset schizophrenia spectrum disorder was observed in 11.2% (41/366). At follow-up, individuals with early-onset reported significantly fewer positive symptoms and were characterised by significantly superior functioning on measures assessing global functioning, social-occupational functioning, and community functioning than individuals with adult-onset. The early-onset group also achieved significantly better vocational outcomes and had a more favourable course of illness with fewer psychotic episodes over the last two years prior to follow-up. Finally, when investigated as a continuous variable, younger age at onset significantly correlated with better symptomatic and functional outcomes. Conclusions: These results question the assumption that early-onset schizophrenia typically has a poor outcome. Early detection and specialised treatment for the first psychotic episode appear to be more effective at improving long-term functional outcomes in people with early-onset schizophrenia as in those with adult-onset schizophrenia. This possibility and the reasons for it need further investigation.