The purpose of the present study was to assess the psychometric properties of the Ottawa Mental Skills Assessment Tool (OMSAT-3), an instrument developed to measure a broad range of mental skills (Salmela, 1992). The OMSAT-3 was administered to 335 athletes from 35 different sports. An initial first-order confirmatory factor analysis (CFA) revealed that the model displayed an inadequate fit, which led to the postulation of a more robust version, the OMSAT-3*. A CFA on this latter version, which included 48 items and 12 mental skill scales grouped under three broader conceptual components—foundation, psychosomatic, and cognitive skills—indicated that the proposed model fit well the data. A second-order CFA assessing the validity of the three broader conceptual components also yielded adequate indices of fit. The OMSAT-3* significantly discriminated between competitive and elite level athletes and its scales yielded acceptable internal consistency and temporal stability. Implications for consultants, coaches, and researchers are discussed.