AbstractObjectiveTo determine the prevalence of co-morbidity of two important global health challenges, anaemia and stunting, among children aged 6–59 months in low- and middle-income countries.DesignSecondary analysis of data from Demographic and Health Surveys (DHS) conducted 2005–2015. Child stunting and anaemia were defined using current WHO classifications. Sociodemographic characteristics of children with anaemia, stunting and co-morbidity of these conditions were compared with those of ‘healthy’ children in the sample (children who were not stunted and not anaemic) using multiple logistic models.SettingLow- and middle-income countries.SubjectsChildren aged 6–59 months.ResultsData from 193 065 children from forty-three countries were included. The pooled proportion of co-morbid anaemia and stunting was 21·5 (95 % CI 21·2, 21·9) %, ranging from the lowest in Albania (2·6 %; 95 % CI 1·8, 3·7 %) to the highest in Yemen (43·3; 95 % CI 40·6, 46·1 %). Compared with the healthy group, children with co-morbidity were more likely to be living in rural areas, have mothers or main carers with lower educational levels and to live in poorer households. Inequality in children who had both anaemia and stunting was apparent in all countries.ConclusionsCo-morbid anaemia and stunting among young children is highly prevalent in low- and middle-income countries, especially among more disadvantaged children. It is suggested that they be considered under a syndemic framework, the Childhood Anaemia and Stunting (CHAS) Syndemic, which acknowledges the interacting nature of these diseases and the social and environmental factors that promote their negative interaction.