Early intervention is assumed to improve outcome in first-episode psychosis, but this has not been proven. OBJECTIVE: To study whether 1-year outcome will be better in a health care sector with early detection (ED) of psychosis compared with sectors with no early detection (no-ED). DESIGN: A quasi-experimental study with ED in 2 experimental sectors and no-ED in 2 control sectors. ED was achieved through low-threshold ED teams and information campaigns about psychosis for the public, schools, and primary health care providers. The ED and no-ED health care areas offered an equivalent assessment and treatment program during the first year. Two hundred and eighty-one patients were included; 88% were reassessed after 1 year. RESULTS: The ED-area patients (N = 141) had a median duration of untreated psychosis of 5 weeks at baseline compared with 16 weeks for patients in the no-ED area (N = 140). Positive and general symptoms, global assessment of functioning, quality of life, time to remission, and course of psychosis at 1 year after the start of treatment were not different between ED and no-ED groups. Outcome was significantly better for the ED area for negative symptoms. CONCLUSIONS: The ED, no-ED differences at baseline become attenuated by 1 year but not the difference in negative symptoms, suggesting secondary prevention in this domain of psychopathology. However, this possibility requires further testing by follow-up and replication.