Objective: To examine the associations between adolescents’ diet quality and their perceived relatives’ and peers’ diet engagement and encouragement. Design: Cross-sectional study performed in European countries. Diet quality was scored using the Diet Quality Index for Adolescents (DQI-A) based on four components: quality, diversity, balance and meal frequency. Perceived diet quality engagement and perceived encouragement of the relatives/peers were assessed using the questions ‘How healthy is each of the following persons’ diet ?’ and ‘How often does each of the following persons encourage you to eat a healthy diet ?’ Setting: Vienna, Ghent, Lille, Athens, Heraklion, Pecs, Rome, Dortmund, Zaragoza and Stockholm. Subjects: Healthy adolescents (n 2943). Results: The perceived engagement level of the mother, father and sister was each positively associated with the DQI-A (P < 0.05). A positive association was found for the perceived engagement level of siblings, father and mother with all specific components (P < 0.05). DQI-A was negatively associated with the perceived encouragement level from a best friend and positively associated with the encouragement level of the mother and father (P < 0.05). Diversity, balance and quality components were positively associated with the perceived encouragement level from the mother and father (P < 0.05), whereas the best friend's perceived encouragement was negatively associated with the meal frequency component (P < 0.01). Conclusions: These findings highlight the role of social engagement and encouragement of relatives and peers in adolescents diet quality. Intervention or promotion programmes aimed at enhancing diet quality in adolescents should target both family and peers.