Using a relatively large adult sample (271 participants in the Minnesota Study of Twins Reared Apart, including 50 pairs of monozygotic and 37 pairs of dizygotic twins), the authors evaluated prior findings of reading, mental ability, and personality correlates of Stroop Color-Word Test (SCWT; J. R. Stroop, 1935) scores. The twin sample allowed the authors to estimate genetic and environmental influences associated with the SCWT scores. No meaningful personality correlates were detected. Genetic influences ranged from 35% for the Interference effect to 53% for the Word score. In spite of significant correlations between the SCWT scores and selected measures of mental ability, genetic influence on SCWT scores was relatively unaffected when the influences of correlated ability measures were removed.