Energy density (ED) is a key dietary characteristic that has been shown to be inversely associated with dietary quality(1) and to influence energy intake in experimental feeding trials(2). As children age, their energy requirements and stomach capacities change, and they may be exposed to a greater variety of foods and beverages through expanding social and physical environments. These factors may lead to differences in food and beverage intake and, therefore, dietary energy density (DED). However, no study has examined DED across childhood and adolescence in Australia. The primary aim of this study was to describe and examine age and sex differences in DED among children and adolescents in Australia. A secondary aim was to explore consumption of low-, medium- and high-energy-density items. This study used 24-hour dietary recall data from child and adolescent participants (aged 2-18 years; n = 2,702) of Australia’s 2011-12 National Nutrition and Physical Activity Survey. DED was calculated as daily energy divided by daily weight of food consumed by the individual (kJ/g). Low-, medium- or high-energy-density items were identified using cut-off values: low ≤4.184 kJ/g, medium >4.184 to <12.552 kJ/g, high ≥12.552 kJ/g(3). Analyses were performed using Stata/SE 15.1 (StataCorp LLC, USA), applying individual sampling weights and replicate weights. Linear regression was used to assess associations between ED and age. Food-only ED was higher among males (7.56 kJ/g) compared to females (7.30 kJ/g; regression coefficient for comparison -0.25 (95% CI -0.46, -0.05); p = 0.018) and increased with age (p < 0.001). ED from food and beverages did not significantly differ between males and females and was not associated with age in males, but there was some association with age in females. The mean percentage of energy intake from low-energy-density items decreased with age (p < 0.001), whereas the mean percentage of energy intake from medium-energy-density items increased with age (p < 0.001). The mean percentage of energy intake from high-energy-density items did not have a clear pattern of change with age. Across age groups, apples, milk, carrots and bananas (except 12-13 years) were consistently among the top five frequently consumed low-energy-density items. White bread, yeast extracts and ham were frequently reported medium-energy-density foods. Butter, cheese and sweet biscuits were frequently reported high-energy-density foods for all age groups. In conclusion, this study found that DED (food-only) increased with age for males and females, which may be explained by a shift in energy intake from low-energy-density foods to medium-energy-density foods across childhood into adolescence. Although some healthy foods were among the most frequently consumed medium- and high-energy-density items, many items were discretionary. These findings highlight the importance of age-appropriate strategies to promote lower-energy-density healthy foods and limit discretionary foods as children transition into adolescence.