The interest in mental health in a sports context has increased in recent years. However, there is no scientifically sound measurement tool for assessing sport-related mental health symptoms in the Finnish language. One of the most frequently used measurement tools for such symptoms in English is the Brunel Mood Scale (BRUMS). The purpose of the present study was to adapt and validate a Finnish version of the BRUMS, referred to as the Finnish Mood Scale (FIMS). The 24-item, 6-factor FIMS was administered to 445 Finnish participants concurrently with Finnish versions of the Depression, Anxiety, and Stress Scale (DASS-21) and the Psychobiosocial States Scale (PBS-S). The sample consisted of 259 females (58.2%), 177 males (39.8%), and 9 who did not disclose their gender (2%), aged 16 to 75 years (M = 35.65, SD = 13.70). Sixty-two participants (13.9%) reported being a competitive athlete, 273 (61.3%) were regular exercisers, and 109 (24.5%) did not exercise regularly. A six-factor modified CFA model indicated an adequate fit to the data (CFI = 0.944, TLI = 0.934, RMSEA = 0.060). Concurrent measures correlated with FIMS in line with theoretical predictions, supporting convergent and divergent validity. Males reported significantly more positive mood scores than females. Physically active participants reported significantly more positive mood scores than inactive individuals, endorsing the mental health benefits of physical exercise. Findings indicate that the FIMS is a suitable measurement tool to screen mood modalities in Finnish populations aged 16 years and older. FIMS may be useful for the early detection of mental ill-health, thus, promoting sustainable mental health.