Based on formulations about the possible consequences for adaptation of gender nonnormative behaviour, we investigated predictive and concurrent relations of hyperactivity and shyness to various aspects of adaptation focusing on possible effects of sex. At ages 5-6, parents and preschool teachers rated hyperactivity and shyness for 151 children (50% boys). At age 9, we obtained teacher ratings of hyperactivity, internalizing and externalizing problems, self-ratings of trait anxiety, and peer nominations of shyness, social preference, and aggression. Several effects of sex were found. Hyperactivity ratings were more strongly related across time and raters for boys than for girls. In the predictive analyses, boys' hyperactivity was more strongly related to aggression than was girls' hyperactivity, and in concurrent analyses, girls' hyperactivity was more strongly associated with low social preference than was boys' hyperactivity. There was a protective effect of shyness with regard to aggression that applied only to boys, that is, at high hyperactivity levels, boys with high shyness levels were less aggressive than boys with low shyness levels. There were also main effects of hyperactivity and shyness. In predictive and concurrent analyses, hyperactivity was associated with low social preference, high levels of externalizing problems and with aggression, whereas shyness was associated with high levels of internalizing problems. Finally, there was an interactive effect of hyperactivity and shyness. In the concurrent analyses, an exacerbating effect was demonstrated insofar as high shyness was associated with low social preference at high, but not at low levels of hyperactivity. The different developmental risks of hyperactivity and shyness were discussed.