The purpose of this study was to examine the effect of the trait shyness and the regulation of emotional expression on close friendship behavior at both cognitive and behavioral level. Two hundred and thirty-one undergraduates (111 males and 120 females) completed a) Trait shyness scale, b) regulation of emotional expression scale, c) self-rated satisfaction of friendship and d) checklist of dyadic behaviors with their close friends. The main results were as follows: i) Shy males were less satisfied and had fewer behaviors with their friends than not-shy males. ii) Shy females had fewer behaviors with their friends than not-shy females. iii) Females who marked a high score on regulation of emotional expression were less satisfied of their friendship than low scorers. iv) Only for males, the interaction effects of trait shyness and regulation of emotional expression on close friendships were partly confirmed. The results indicate that trait shyness has negative effects on both dyadic behavior of friendship and friendship satisfaction though excessive emotion expression has negative effects only on friendship satisfaction.
