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Background The Composite Index of Anthropometric Failure (CIAF) and its extensions-the Composite Index of Severe Anthropometric Failure (CISAF) and extended CIAF (eCIAF)—capture overlapping forms of child undernutrition but remain under-reported at global and regional levels. We aimed to estimate the prevalence of CIAF, CISAF and eCIAF among children under 5 years and assess inequalities by sex, residence, household wealth and maternal education.Methods We systematically searched major databases, including Embase, MEDLINE (PubMed), Scopus, CINAHL, ProQuest, Global Index Medicus and the Cochrane Library, without language or geographic restrictions. Random-effects meta-analyses estimated pooled prevalence. Heterogeneity was assessed using Cochran’s Q and I² statistics. Subgroup analyses, meta-regression, sensitivity analyses and publication bias assessments were conducted. Inequalities were quantified using prevalence ratios (PRs), prevalence differences, the Concentration Index and the Slope Index of Inequality (SII).Results We included 107 studies from 18 countries, predominantly low- and middle-income countries in South Asia and Africa (notably India, n=54), comprising over 2.6 million under-5 children for CIAF, 590 744 for eCIAF and 29 905 for CISAF. The pooled prevalence of CIAF was 49.07% (95% CI 46.00% to 52.14%), declining from 59.8% in 2005 to 45.9% in 2024. The pooled prevalence of CISAF and eCIAF was 12.77% and 40.41%, respectively. CIAF prevalence did not differ significantly by sex (pooled PR: 1.04, 95% CI 0.99 to 1.09) but was higher in rural than in urban settings (pooled PR: 1.18, 95% CI 1.10 to 1.27). Substantial socioeconomic inequalities were observed, with higher prevalence among children from the poorest households (pooled PR: 1.71, 95% CI 1.42 to 2.05) and among those whose mothers had no formal education (pooled PR: 1.55, 95% CI 1.26 to 1.90). Absolute inequalities were further confirmed by SII estimates for wealth (−31.28%) and maternal education (−26.60%).Conclusions CIAF prevalence remains alarmingly high in low-income settings, disproportionately affecting children in rural areas, poorer households and those born to mothers with limited education.