During adolescence, physical activity (PA) decreases with potentially serious, long-term consequences for physical and mental health. Although barriers have been identified as an important PA correlate in adults, research on adolescents’ PA barriers is lacking. Thus reliable, valid scales to measure adolescents’ PA barriers are needed. We present two studies describing a broad range of PA barriers relevant to adolescents with a multidimensional approach. In Study 1, 124 adolescents (age range = 12 – 24 years) reported their most important PA barriers. Two independent coders categorized those barriers. The most frequent PA barriers were incorporated in a multidimensional questionnaire. In Study 2, 598 adolescents (age range = 13 – 21 years) completed this questionnaire and reported their current PA, intention, self-efficacy, and negative outcome expectations. Seven PA barrier dimensions (leisure activities, lack of motivation, screen-based sedentary behavior, depressed mood, physical health, school workload, and preconditions) were confirmed in factor analyses. A multidimensional approach to measuring PA barriers in adolescents is reliable and valid. The current studies provide the basis for developing individually tailored interventions to increase PA in adolescents.