Background: Autism Spectrum Disorder (ASD) is characterised by altered social patterns, often associated with increased stress. While puberty is associated with increased stress, there is limited research on stress response to social interaction in adolescents with ASD. The study investigated stress response to semi-structured, videogame-based interaction in adolescents with and without ASD, and the impact of puberty. Method: Twelve adolescents with ASD and 12 typically developing (TD) peers participated in a semi-structured, videogame-based social interaction. Stress was measured via salivary cortisol. Results: There were no significant between-group differences in cortisol. Pubertal development was correlated with cortisol in ASD (r = 0.85, p < 0.001), but not TD (r = 0.03, p = 0.94). Conclusions: Findings contribute to a fuller picture of the developmental trajectories of physiological stress in ASD, including the importance of context, structure, and puberty. The current investigation underscores the necessity of incorporating varied social contexts when assessing stress and social interaction.