Grounded within self-determination theory (SDT; Deci & Ryan, 2000; Ryan & Deci, in press), three studies were conducted to develop and psychometrically test a measure of adolescents’ perceptions of psychological need support for exercise (viz., for autonomy, competence, and relatedness): the Adolescent Psychological Need Support in Exercise Questionnaire (APNSEQ). In Study 1, 34 items were developed in collaboration with an expert panel. Through categorical confirmatory factor analysis and item response theory, responses from 433 adolescents were used to identify the best fitting and performing items in Study 2. Here, a three-factor nine-item measure showed good fit to the data. In Study 3, responses from an independent sample of 373 adolescents provided further evidence for the nine-item solution as well as for internal consistency, criterion validity, and invariance across gender and social agent (friends, family, and physical education teacher). The APNSEQ was supported as a measure of adolescents’ perceptions of psychological need support within the context of exercise.