Changes in intimate friendship with same-sex and opposite-sex friends in preadolescence and adolescence were investigated using Sharabany's Intimacy Scale. The sample consisted of 480 Israeli children from the 5th, 7th, 9th, and llth grades who rated their friendship with a same-sex or opposite-sex best friend. There was a significant age difference in overall intimacy with same-sex friends. Frankness and spontaneity, knowing and sensitivity, attachment, exclusiveness, and giving and sharing were dimensions that exhibited change with age. Trust and loyalty, and taking and imposing did not. Opposite-sex friendship revealed a significant increase in intimacy with age. Boys and girls did not differ in reported opposite-sex friendship in the 5th and 7th grades, whereas girls in the 9th and llth grades reported higher intimacy than did boys. This sex-by-age pattern of interaction was particularly evident for attachment and for trust and loyalty. Girls were higher in knowing and sensitivity, giving and sharing, and taking and imposing. The implications for further differentiation among types of peer relations and interrelation of dyadic friendship and cognitive growth are discussed.The importance of peer relations for the normal social development of the individual has been documented. Studies relate to experiments with animals (e.g., Harlow, 1971;Suomi, 1978), schizophrenic adults (e.g., Pitt, Kornfeld, &Kolb, 1963), and young children (e.g., Freud & Dann, 1951). Most studies, however, including those that used the term friendship, focused mainly on acceptability and isolation among peers (see reviews in Hartup 1970Hartup , 1978Hartup , 1979. Few studies examined the nature of enduring meaningful relations proper, such as children's expectations of their friends (