Frequent consumption of energy-dense foods has been strongly implicated in the global increase of obesity. The World Cancer Research Fund suggests a population-level energy density (ED) goal for diets of 523 kJ/100 g (125 kcal/100 g) as desirable for reducing weight gain and related co-morbidities. However, there is limited information about the ED of diets of contemporary populations. The aims of the present study were to (1) estimate the mean ED of the Scottish diet, (2) assess differences in ED over time by socio-economic position, by household (HH) composition and for HH meeting dietary targets for fat and fruit and vegetables, and (3) assess the relationship between ED and the consumption of foods and nutrients, which are indicative of diet quality. ED of the diet was estimated from food (including milk) from UK food purchase survey data. The average ED of the Scottish diet was estimated as 718 kJ/100 g with no change between the survey periods 2001 and 2009. Individuals living in the most deprived areas had a higher mean ED than those living in the least deprived areas (737 v. 696 kJ/100 g). Single-parent HH had the highest mean ED (765 kJ/100 g) of all the HH surveyed. The mean ED of HH achieving dietary targets for fat and fruit and vegetables was 576 kJ/100 g compared with 731 kJ/100 g for non-achievers. HH within the lowest quintile of ED were, on average, closest to meeting most dietary guidelines. Food purchase data can be used to monitor the quality of the diet in terms of dietary ED of the population and subgroups defined by an area-based measure of socio-economic status.