Purpose: To estimate the 10-year change in the overall nutritional quality of adolescent and young adult’s diet, as measured by the modified Nutrient Profiling System of the British Food Standards Agency individual Dietary Index (FSAm-NPS-DI) which funds the Nutri-Score development, and in different components of this score, overall and according to the individual characteristics. Methods: Two 24-h dietary recalls were carried out in 15- to 39-year-old respondents included in the Belgian Food Consumption Surveys in 2004 (n = 1186) and 2014 (n = 952). The weighted mean individual FSAm-NPS-DI was computed from all foods and beverages consumed, converted into a scale from 0 to 100 (from the poorest to the most favorable diet), and compared between survey years. Subject characteristics associated with the score, along with the mean daily intake of food groups, energy, and nutrients were explored in multiple linear regressions stratified by survey year and age group. Results: The weighted mean daily FSAm-NPS-DI significantly increased between 2004 and 2014 [2004: 55.3 (SEM: 0.2) vs. 2014: 57.4 (0.5), P < 0.001 in 15- to 18-year olds; 55.0 (0.6) vs. 58.1 (0.4), P < 0.001 in 19- to 25-year olds; 57.1 (0.4) vs. 58.5 (0.3), P < 0.01 in 26- to 39-year olds]. SFA intake decreased in all age groups, and sugar-sweetened beverage, sugar, sodium, and fiber intakes decreased among 15‒18-year olds. The nutritional quality changed unevenly according to sociocultural characteristics, levels of education and regions being the main sources of disparities. Conclusion: The quality of diet improved overall between 2004 and 2014 among young people in Belgium, an uneven change that need to be confirmed in future surveys, following the implementation of the Nutri-Score. ; SCOPUS: ar.j ; info:eu-repo/semantics/published