Self-determination theory (SDT) has become an established framework for exploring motivational processes in physical exercise. The integral components of SDT are three basic psychological needs. For our study we translated and validated a German scale that measures need satisfaction in exercise. A total of 614 individuals (n = 347 female, age: M = 38.39 years, SD = 12.05) recruited from a private fitness center, various sport clubs, and the Academic Sports Association Zurich, Switzerland, took part in the online-based baseline assessment (T1). Nine months later, 216 participants completed the online follow-up questionnaire (T2). The results demonstrate adequate factor validity and internal consistency at both measurement points. Moreover, construct validity was demonstrated by medium to strong correlations of several motives to exercise and the self-efficacy of physical exercise. In addition, the three subscales were differentially predictive for different types of motivation (for example, intrinsic and extrinsic) at T2, indicating good criterion validity. The newly developed German scale is a reliable and valid instrument for assessing need satisfaction in the context of physical exercise and predicting motivation over time.