A study was conducted to examine the association between the personality trait social introversion, measured by peer ratings, and performance on a test of spatial reasoning, the Block Design subtest of the Wechsler Adult Intelligence Scale. The subjects were 63 men from social fraternities at a state university. Social introversion and performance on the Block Design test correlated r = .72, p < .001, indicating a substantial association between these seemingly dissimilar measures of performance. Inasmuch as both variables have high heritability coefficients, it is possible they have a common genetic influence.