BackgroundLower energy density diets tend to cost more, but data using different ways to calculate the dietary energy density, is scarce. ObjectivesTo estimate the dietary energy density, and to assess how it is associated with the diet cost in children. MethodsData were obtained from a community-based survey from public elementary schools in Portugal. Dietary intake of 464 children (6–12 years) was assessed by a 24h recall in 2007/2008. Dietary energy density (kcal/g) was calculated as following: (1) with food and all beverages (ED1), (2) with food and caloric beverages (ED2), and (3) only with food (ED3). Energy-adjusted diet cost (€/1000kcal) was calculated based on the collection of food prices from a national leader supermarket. Anthropometric measures were taken and socio-demographic data were obtained from parents. Logistic regression was used to estimate the association between diet cost and energy density. ResultsFor boys, the energy-adjusted diet cost of the highest third of energy density was lower, between 81% in the ED3 (p for trend <0.001) and 87% in the ED1 (p for trend <0.001), compared to the lowest third. Girls showed similar, but weaker associations. ConclusionsHigher dietary energy density was associated with lower dietary cost among children.