The relationship between handedness and cognitive function varies across studies, perhaps partly due to the many medical and psychiatric conditions with known cognitive impact. This study examined cognitive performance in 643 healthy individuals (age 5-82) who were categorized as strongly right-handed, moderately right-handed, or left/mixed-handed. Cognitive differences emerged, as left/mixed-handed individuals demonstrating superior psychomotor speed and cognitive flexibility, and strongly and moderately right-handed individuals exhibiting better time estimation skills. No interaction-among handedness, sex, and age were found. These findings indicate cognitive differences associated with handedness exist independent of medical and psychiatric confounds. Further work is needed to clarify these findings.