BackgroundGlobally, the co-occurrence of stunting and overweight or obesity (CSO) in the same individual is becoming an emerging layer of malnutrition and there is a paucity of information in low- and middle-income countries, particularly in sub-Saharan Africa. Hence, this study aimed to determine the pooled prevalence and determinants of concurrent stunting and overweight or obesity among under-five children in SSA.MethodsSecondary data analysis was conducted from a recent nationally representative Demographic and Health Survey dataset of 35 SSA countries. A total weighted sample of 210,565 under-five children was included in the study. A multivariable multilevel mixed effect model was employed to identify the determinant of the prevalence of under-5 CSO. The Intra-class Correlation Coefficient (ICC) and Likelihood Ratio (LR) test were used to assess the presence of the clustering effect. A p-value ofp < 0.05was used to declare statistical significance.ResultThe pooled prevalence of concurrent stunting and overweight/obesity among under-five children was 1.82% (95% CI: 1.76, 1.87) in SSA. Across the SSA regions, the highest prevalence of CSO was reported in Southern Africa (2.64%, 95% CI: 2.17, 3.17) followed by the Central Africa region (2.21%, 95% CI: 2.06, 2.37). Under five children aged 12–23 months (AOR = 0.45, 95% CI: 0.34, 0.59), 24–35 months (AOR = 0.41, 95% CI: 0.32, 0.52), 36–59 months (AOR = 055, 95% CI: 0.43, 0.70), ever had no vaccination (AOR = 1.25, 95% CI: 1.09, 1.54), under-five children born from 25 to 34 years mother (AOR = 0.75, 95% CI: 0.61, 0.91), under-five children born from overweight/obese mothers (AOR = 1.63, 95% CI: 1.14, 2.34), and under-five children living in West Africa (AOR = 0.77, 95% CI: 0.61, 0.96) were significant determinants for under-five CSO.ConclusionConcurrent stunting and overweight or obesity is becoming an emerging layer of malnutrition. Under five children born in the SSA region had almost a 2% overall risk of developing CSO. Age of the children, vaccination status, maternal age, maternal obesity, and region of SSA were significantly associated with under-five CSO. Therefore, nutrition policies and programs should base on the identified factors and promote a quality and nutritious diet to limit the risk of developing CSO in early life.