Background Concurrent wasting and stunting (WaSt) is a severe form of child undernutrition, linked to higher mortality and long-term negative health outcomes. Malnutrition is a significant challenge in Yemen, where the country is experiencing a long-standing conflict, food insecurity, and socioeconomic deprivation. But there is still limited evidence on the burden and determinants of WaSt in Yemen on a national level. This study aimed to estimate the prevalence and identify factors associated with WaSt among children under 5 years in Yemen. Methods We conducted a cross-sectional analysis using nationally representative data from the 2022-2023 Yemen Multiple Indicator Cluster Survey (MICS). A significantly large dataset of 17,734 children aged 0-59 months from all the 22 governorates of Yemen was analyzed. Concurrent wasting and stunting (WaSt) was defined as the coexistence of a weight-for-height z-score (WHZ) below -2 standard deviations and a height-for-age z-score (HAZ) below -2 standard deviations from the WHO Child Growth Standards in the same child. Survey-weighted logistic regression was performed to analyze the factors associated with WaSt among the under 5 children in Yemen. Results The national prevalence of WaSt was 8.4% (95% CI: 7.6-9.2). The highest prevalence of WaSt was found in children aged 12-23 months (12.0%) and in the Western Coastal region (11.6%). After adjustment, male sex (AOR 1.52, 95% CI: 1.30-1.80), residence in the Western Coastal (AOR 2.00, 95% CI: 1.60-2.40), Eastern (AOR 2.00, 95% CI: 1.50-2.70), and Southern regions (AOR 1.60, 95% CI: 1.20-2.10), poorest household wealth (AOR 1.96, 95% CI: 1.30-2.90), moderate (AOR 1.51, 95% CI: 1.13-1.94) and severe food insecurity (AOR 1.94, 95% CI: 1.40-2.60), and recent diarrhoea (AOR 1.22, 95% CI: 1.02-1.44) were associated with higher odds of WaSt. Having a handwashing facility and improved sanitation were protective. Conclusion At least 1 in every 12 under-five children in Yemen was affected by WaSt, and there were significant socioeconomic, geographic, food-security and WASH-related factors influencing this devastating outcome. Instead of simple, one-dimensional approaches, multi-sectoral interventions are needed to address this adversity. And those efforts must be integrated into the system, interconnected with each other and specifically targeted to vulnerable children and households.