Two populations of phenotypic males, twelve 47,XYY and twelve 47,XXY patients, when compared for behavior disability, sexual practices, and social interaction, revealed that the XYY males had behavior disability involving a predominance of impulsive acting out and poor long term planning. By contrast, the XXY males manifested a deficiency or inhibition of action. With regard to sexual practices, the XYY males reported a greater frequency and diversity of sexual experience and imagery than did the XXY males, who appear to be sexually inert by comparison. For both XYY and XXY men, being alone took preference over group participation. The XXY men were more characterized by inertia and reclusiveness, while the XYY men were mobile and more likely to intrude on other people and their property.