Background Adolescence is marked by increases in autonomy, establishment of health behaviors, and changes in self-regulation. Numerous facets of adolescents' eating behavior occur in the context of increased autonomy, including food choices when apart from parents/caregivers, on weekend times with less structure than the school week, and during snacking occasions (versus meals). While previous studies have examined situations with assumed autonomy differences, ours is the first to directly examine eating autonomy in adolescents' food choices, using a momentary design.Purpose The purpose of this study was to examine the construct of eating autonomy through smartphone-based ecological momentary assessment (EMA).Methods Over seven days, adolescents (n = 48; 12-17y) reported their perceived control in selecting recent food/drinks alongside contextual data from each eating occasion. We hypothesized that, within-subjects, eating autonomy would be higher on weekends, during snacks, and when eating with friends/peers compared to weekdays, during meals, and eating with parents respectively. We also hypothesized that there would be between-subjects differences in adolescents' eating autonomy by age and gender.Results Generalized Linear Mixed Models (GLMM) analyses found within-subjects effects showing higher autonomy during snacks and when eating alone, whereas autonomy decreased when eating with parents and during after-school and dinnertimes. There was no significant association between age and eating autonomy.Conclusions These findings suggest that adolescents demonstrate significant autonomy over food choices, that varies by social context, type of eating occasion, and time of day. Understanding these patterns can inform adolescent-focused and parental support interventions aimed at improving adolescents' dietary behaviors by targeting specific contexts where autonomy is greater. The insights gained from this study can help shape strategies that promote healthier eating habits among adolescents by enhancing their decision-making autonomy in various contexts. Adolescents experienced more eating autonomy when eating alone and/or apart from parents and during snacking occasions, but eating autonomy did not differ by age group, gender, or day of the week. Adolescence is believed to be a critical period for establishing adult eating patterns. While adolescents are thought to have increased autonomy, or independence, over their eating behaviors with age, previous studies have not tried to directly measure autonomy in eating behaviors. The purpose of this study was to directly examine eating autonomy in adolescents' food choices, using an ecological momentary assessment design. This smartphone-based study collected data from forty-eight adolescents (ages 12-17y). They reported on their perceived control when selecting food/drinks throughout the day over 7 days, along with contextual data (like who was with them) from each eating occasion. We believed adolescents' eating autonomy would be higher for females, older teens, on weekends (compared to weekdays), during snacks (compared to meals), and when eating with friends/peers (compared to parents). Our analysis found that adolescents had higher autonomy during snacks and when eating alone, whereas autonomy decreased when eating with parents and during after-school and dinnertimes. However there was no relationship between age or gender and eating autonomy. These findings suggest that adolescents have significant autonomy over food choices, that varies by social context, type of eating occasion, and time of day.