Literature on sex differences in impulsivity has tended to focus on differences between groups, while ignoring relationships beyond zero order correlations. The purpose of this study was to evaluate Maccoby's hypothesis (1966) of opposite-direction correlations where the relationship between a set of variables (e.g., impulsivity and intellectual ability) is curvilinear, with males and females being systematically distributed on opposite sides of the curve. The Primary Mental Abilities (PMA) and Matching Familiar Figures tests were administered to 44 males and 49 females. The relationship between all of the PMA subtests and impulsivity was curvilinear for males, but linear for females on all but one of the subtests. The importance and implications of examining distribution differences rather than group differences are discussed.Support for this study has come from the Office of Research Administration, University of Kansas, Grant Number 3581-5038. This paper was presented in part at the meeting of the American Psychological Association, Chicago, August 1975, Division 7.