Objective: The current study is an attempt to explore under-five child malnutrition in a low-income population setting using the Extended Composite Index of Anthropometric Failure (ECIAF). Design: Data from the Bangladesh Demographic and Health Survey 2017-2018 were analysed. Malnutrition using ECIAF was estimated using stunting, wasting underweight and overweight. Multilevel logistic regression models identified factors associated with malnutrition. Geospatial analysis was conducted using R programming. Setting: Bangladesh. Participants: Children under 5 years of age. Results: In Bangladesh, as indicated by the ECIAF, approximately 40<middle dot>8 % (95 % CI: 39<middle dot>7, 41<middle dot>9) of children under five experience malnutrition, whereas about 3<middle dot>3 % (95 % CI: 2<middle dot>9, 3<middle dot>7) were overweight. Children of parents with no formal education (56<middle dot>3 %, 95 % CI: 50<middle dot>8, 61<middle dot>8), underweight mothers (53<middle dot>4 %, 95 % CI: 50<middle dot>4, 56<middle dot>3), belonging to the lowest socio-economic strata (50<middle dot>6 %, 95 % CI: 48<middle dot>3, 53<middle dot>0), residing in rural areas (43<middle dot>3 %, 95 % CI: 41<middle dot>9, 44<middle dot>6) and aged below 3 years (47<middle dot>7 %, 95 % CI: 45<middle dot>2, 50<middle dot>2) demonstrated a greater age- and sex-adjusted prevalence of malnutrition. The Sylhet division (Eastern region) exhibited a higher prevalence of malnutrition (> 55<middle dot>0 %). Mothers with no formal education (adjusted OR (AOR): 1<middle dot>51, 95 % CI: 1<middle dot>08, 2<middle dot>10), underweight mother (AOR: 1<middle dot>54, 95 % CI: 1<middle dot>03, 1<middle dot>83), poorest socio-economic status (AOR: 2<middle dot>14, 95 % CI: 1<middle dot>64, 2<middle dot>81), children aged 24-35 months (AOR: 2<middle dot>37, 95 % CI: 1<middle dot>97, 2<middle dot>85) and fourth and above birth order children (AOR: 1<middle dot>41, 95 % CI: 1<middle dot>16, 1<middle dot>72) were identified key factors associated with childhood malnutrition while adjusting community- and household-level variations. Conclusions: In Bangladesh, two out of five children were malnourished, and one in thirty-five children was overweight. Continuous monitoring of the ECIAF over time would facilitate tracking changes in the prevalence of different forms of malnutrition, helping to plan interventions and assess the effectiveness of interventions aimed at addressing both undernutrition and overweight.