PURPOSE OF REVIEW: It has been hypothesized that the first 5 years after first episode of psychosis are a critical period with opportunities for ameliorating the course of illness. On the basis of this rationale, specialized assertive early intervention services were developed. We wanted to investigate the evidence basis for such interventions. RECENT FINDINGS: The evidence for the effectiveness of specialized assertive early intervention services is mainly based on one large randomized clinical trial, the OPUS trial, but it is supported by the findings in smaller trials, such as the Lambeth Early Onset trial, the Croydon Outreach and Assertive Support Team trial and the Norwegian site of Optimal Treatment trial. There are positive effects on psychotic and negative symptoms, on substance abuse and user satisfaction, but the clinical effects are not sustainable when patients are transferred to standard treatment. However, the positive effects on service use and ability to live independently seem to be durable. SUMMARY: Implementation of specialized assertive early intervention services is recommended, but the evidence basis needs to be strengthened through replication in large high-quality trials. Recommendation regarding the duration of treatment must await results of ongoing trials comparing 2 years of intervention with extended treatment periods.