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Background: The importance of physical activity (PA) and related social inequalities in the prevention and management of obesity is discussed. Our objective was to identify, within the PRALIMAP-INÉS programme, the determinants of participation of overweight adolescents from a disadvantaged background. Methods: Five group sessions including two PA-specific sessions, and individual activities adapted to the social situation were conducted by dieticians, psychologists and PA practitioners. These activities were proposed to 411 overweight and obese adolescents from a low socioeconomic background, aged 13 to 18 years and participating in PRALIMAP-INÉS in 35 schools in the Vosges department. Results: Higher participation rates in at least one group session were observed among middle school students compared to high school students (OR=2.2), and those who reported financial difficulties in paying a license (OR=5.8). The mean number of sessions increased with body mass index, was higher among middle school students (+0.7 session) and lower among those reporting financial difficulties (–1.1 session). Participation rates in a PA interview were significantly higher among girls (OR=1.8), in those who participated in the National Union School Sport (OR=2.4) and those who reported having no friends to practice (OR=2.7). The level of PA and sedentary behaviour were not associated with participation. Conclusions: Initial participation in PRALIMAP-INÉS group activities was high among disadvantaged teenagers with financial difficulties, but it was more difficult to maintain their participation throughout the programme. Identification of factors that can maintain participation is a major challenge for continuity of the programme.