This study developed a psychometrically sound measure of closeness in Australian men's (n = 59) and women's (n = 77) same-sex friendships, the Friendship Closeness Inventory. Subscales were developed to measure both masculine and feminine styles of closeness in three domains of Emotional Closeness, Behavioural Closeness, and Cognitive Closeness. The inventory was subjected to reliability checks which supported the reliability of each scale, and factor analyses which supported the 3-factor design. Correlations among ratings on subscales suggested that the affective, behavioural, and cognitive dimensions are distinguishable but related components of friendship. Group comparisons indicated that women rated themselves closer to their same-sex friends on the affective dimension than men. Researchers have suggested that sex-role socialisation may partly account for sex differences in self-ratings of emotional expressiveness in friendships. There were no significant differences between men's and women's ratings on the behavioural and cognitive aspects of friendships. The cognitive element may need further exploration in further scale development as it measures only one aspect of cognitive closeness: the perceived influence of friends. Pending further validation, the inventory appears potentially useful for research exploring affective, behavioural, and cognitive elements of young men's and women's friendships.