The development process and initial validation of the Basic Psychological Needs in Exercise Scale (BPNES) are presented in this study. The BPNES is a domain-specific self-report instrument designed to assess perceptions of the extent to which the innate needs for autonomy, competence, and relatedness (Deci & Ryan, 2000) are satisfied in exercise. Two separate samples of 508 and 504 participants were employed from private fitness centers for scale calibration and validation purposes, respectively. The results demonstrated an adequate factor structure, internal consistency, generalizability of the factor dimensionality across the calibration and the validation samples, discriminant validity and predictive validity; acceptable stability of the BPNES scores over 4 weeks also was found. In addition, the scale scores were found to be largely unaffected by socially desirable responding and specifically the tendency for impression management. (Contains 1 footnote and 4 tables.)