AbstractDuration of untreated psychosis (DUP) has been associated with poor mental health outcomes. We aimed to meta-analytically estimate the mean and median DUP worldwide, evaluating also the influence of several moderating factors. This PRISMA/MOOSE-compliant meta-analysis searched for non-overlapping individual studies from inception until 9/12/2022, reporting mean ± s.d. or median DUP in patients with first episode psychosis (FEP), without language restrictions. We conducted random-effect meta-analyses, stratified analyses, heterogeneity analyses, meta-regression analyses, and quality assessment (PROSPERO:CRD42020163640). From 12 461 citations, 369 studies were included. The mean DUP was 42.6 weeks (95% confidence interval (CI) 40.6–44.6, k = 283, n = 41 320), varying significantly across continents (p < 0.001). DUP was (in descending order) 70.0 weeks (95% CI 51.6–88.4, k = 11, n = 1508) in Africa; 48.8 weeks (95% CI 43.8–53.9, k = 73, n = 12 223) in Asia; 48.7 weeks (95% CI 43.0–54.4, k = 36, n = 5838) in North America; 38.6 weeks (95% CI 36.0–41.3, k = 145, n = 19 389) in Europe; 34.9 weeks (95% CI 23.0–46.9, k = 11, n = 1159) in South America and 28.0 weeks (95% CI 20.9–35.0, k = 6, n = 1203) in Australasia. There were differences depending on the income of countries: DUP was 48.4 weeks (95% CI 43.0–48.4, k = 58, n = 5635) in middle-low income countries and 41.2 weeks (95% CI 39.0–43.4, k = 222, n = 35 685) in high income countries. Longer DUP was significantly associated with older age (β = 0.836, p < 0.001), older publication year (β = 0.404, p = 0.038) and higher proportion of non-White FEP patients (β = 0.232, p < 0.001). Median DUP was 14 weeks (Interquartile range = 8.8–28.0, k = 206, n = 37 215). In conclusion, DUP is high throughout the world, with marked variation. Efforts to identify and intervene sooner in patients with FEP, and to promote global mental health and access to early intervention services (EIS) are critical, especially in developing countries.