The State-Trait Cheerfulness Inventory–Trait Version (STCI-T60) measures the temperamental basis of sense of humor involving theoretically derived personality dispositions of cheerfulness, seriousness, and bad mood. The reliability and validity of the newly developed STCI-T60 Italian version were assessed in a sample of Italian speakers ( N = 683). Proper fit for a three-dimensional factor structure observed in previous studies was replicated and each factor demonstrated acceptable internal consistency and test–retest reliability. The associations between the STCI subscales and major personality dimensions, optimism, resilience, stress, and general well-being were further examined and results were in the expected directions (e.g., cheerfulness and bad mood being positively and negatively associated with well-being variables, respectively). Cross-cultural invariance examination was conducted to provide more validity data for the Italian STCI. Metric invariance was found between Italian and Canadian English speakers ( N = 632), but scalar invariance was not shown.