BACKGROUND: People with affective psychotic disorders often face diagnostic delays and presentations are under-recognised at first contact with early intervention services (EIS). Despite their clinical significance, most research and service models for first-episode psychosis (FEP) have focused on non-affective psychoses. AIMS: We sought to clarify the relative prevalence of affective psychoses in EIS. METHOD: A systematic review and random-effects meta-analysis of observational studies reporting proportion of affective psychotic disorders among individuals presenting to EIS with FEP was conducted. Eligible studies included treated FEP populations diagnosed using DSM/ICD criteria. Searches were conducted in Web of Science, Medline and PsycINFO (inception to July 2025). The primary outcome was pooled proportion of affective psychotic disorders. Heterogeneity was assessed using Q-statistics and I2-statistics. Meta-regressions examined potential moderators, including urbanicity, national income level and geographical region. RESULTS: Eighty-three studies (N = 30 946; mean age 24.95 years; 34.78% female) were included. Random-effects pooled proportion was 18.0% (95% CI 15.4-20.6; 95% prediction interval 3.6-39.4%; I2 = 95.6%). Schizoaffective disorder represented 7.4% (k = 49; 95% CI 5.8-9.2). Schizophrenia was the most frequent diagnosis, with a pooled proportion of 45.5% (k = 79; 95% CI 40.3-50.7). Meta-regression analyses identified that affective psychoses were less common in Asia and more common in North America compared with Europe. Higher urbanicity was also associated with increased prevalence. Associations with national income level (NIL) were limited by small subgroup sizes. CONCLUSIONS: Affective psychotic disorders constitute a meaningful subgroup within EIS. This suggests better screening, targeted treatments and adaptive service models of care.