BACKGROUND: Information about the cost-effectiveness of early intervention programmes for first-episode psychosis is limited. AIMS: To evaluate the cost-effectiveness of an intensive early-intervention programme (called OPUS) (trial registration NCT00157313) consisting of enriched assertive community treatment, psychoeducational family treatment and social skills training for individuals with first-episode psychosis compared with standard treatment. METHOD: An incremental cost-effectiveness analysis of a randomised controlled trial, adopting a public sector perspective was undertaken. RESULTS: The mean total costs of OPUS over 5 years (e123 683, s.e. = 8970) were not significantly different from that of standard treatment (e148 751, s.e. = 13073). At 2-year follow-up the mean Global Assessment of Functioning (GAF) score in the OPUS group (55.16, s.d. = 15.15) was significantly higher than in standard treatment group (51.13, s.d. = 15.92). However, the mean GAF did not differ significantly between the groups at 5-year follow-up (55.35 (s.d. = 18.28) and 54.16 (s.d. = 18.41), respectively). Cost-effectiveness planes based on non-parametric bootstrapping showed that OPUS was less costly and more effective in 70% of the replications. For a willingness-to-pay up to e50 000 the probability that OPUS was cost-effective was more than 80%. CONCLUSIONS: The incremental cost-effectiveness analysis showed that there was a high probability of OPUS being cost-effective compared with standard treatment.