To assess ethnicity- and age-modified associations between mid-upper arm circumference (MUAC) and mortality in Nepalese children and whether sociodemographic factors explain these associations.

Secondary data analysis of children followed until 3 years of age. Estimated mortality hazard ratios (HR) for MUAC<11·5cm (recommended cut-off for identifying severe acute malnutrition among children ≥6 months old) compared with ≥11·5cm in younger (<6 months) and older children (≥6 months) of Pahadi and Madhesi ethnicity, adjusting for sex, socio-economic status (SES) and mother’s education using Cox proportional hazard models.

Sarlahi, Nepal (21 October 2001–2 February 2006).

Children (n 48 492) enrolled in the Nepal Nutrition Intervention Project, Sarlahi-4.

Among children aged ≥6 months, MUAC<11·5 cm was associated with increased risk of mortality in both Pahadis (HR=4·01; 95 % CI 1·42, 11·76) and Madhesis (HR=5·60; 95 % CI 3·87, 8·11) compared with those with MUAC≥11·5 cm, after adjusting for sex, SES and maternal literacy. Among children <6 months old, MUAC<11·5 cm was not associated with mortality in Pahadis with (HR=1·12; 95 % CI 0·72, 1·73) or without adjusting (HR=1·17; 95 % CI 0·75, 1·18) as compared with Madeshis (adjusted HR=1·76; 95 % CI 1·35, 2·28).

Among older children, MUAC<11·5 cm is associated with subsequent mortality in both ethnicities regardless of other characteristics. However, among children aged <6 months, it predicted mortality only among Madhesis, while sociodemographic factors were more strongly associated with mortality than MUAC<11·5cm among Pahadis.