The satisfaction of adolescents' perceived psychological needs facilitates their academic achievement and adjustment within school. A first step in this direction is the identification of adolescents' psychological needs and the environmental factors to meet these needs. Based on the theory of Existence, Relatedness, and Growth, known as ERG, the present study aimed to develop and provide evidence for the validity of a new measure of adolescent students' psychological needs at school. Five hundred and eighty adolescent students of public secondary schools in central Greece participated in the study. Students completed the ERG Needs Scale, the Autonomy and Competence Scales, and the Subjective Well-Being measures. Preliminary results showed that the new instrument has promising psychometric properties. The potential contribution of the new instrument for future research and educational practices are discussed.