Objective: To assess the relationship(s) between overall and within-food group diversity and several indices of dietary quality, such as dietary adequacy, moderation and balance, in Belgian adults. Dietary quality indices were derived from the food-based dietary guidelines (FBDG). Design: Information on food intake was collected with two 24 h recalls. Setting: Average overall and within-food group diversity scores and dietary adequacy, moderation and balance scores were calculated. Subjects: A representative sample (n 3245) of the Belgian population at the age of 15 years and older was randomly selected from the National Register using a multistage stratified procedure. Results: For both men and women, total dietary diversity score increased with age and smokers had a significantly lower overall diversity score than non-or former smokers. A positive association was found between overall dietary diversity and both dietary adequacy and balance. For most food groups, especially bread and cereals, vegetables, dairy products and spreadable fats, within-food group dietary diversity was positively associated with the fulfilment of the specific recommendation for the intake of that food group. An inverse association was found between dietary diversity within the meat and the energy-dense, nutrient-poor food groups and dietary balance. Diversity within the dairy and spreadable fat group was responsible for the strongest increase in overall dietary adequacy and balance. Conclusions: Overall dietary diversity is a useful indicator of dietary quality in Belgium. For some food groups, within-food group dietary diversity is a useful indicator of compliance with the specific FBDG for intake of that food group.