This study examined the utility of modifying the Social Anxiety Scale for Children-Revised (SASC-R) for use with adolescents, and examined associations between adolescents' social anxiety (SA) and their peer relations, friendships, and social functioning. Boys (n = 101) and girls (n = 149) in the 10th through 12th grades completed the Social Anxiety Scale for Adolescents (SAS-A) and measures of social support, perceived competence, and number and quality of their best friendships. Factor analysis of the SAS-A confirmed a three-factor structure: Fear of Negative Evaluation, Social Avoidance and Distress in General, and Social Avoidance Specific to New Situations or Unfamiliar Peers. Girls reported more SA than boys, and SA was more strongly linked to girls' social functioning than boys'. Specifically, adolescents with higher levels of SA reported poorer social functioning (less support from classmates, less social acceptance), and girls with higher levels of SA reported fewer friendships, and less intimacy, companionship, and support in their close friendships. These findings extend work on the SASC-R to adolescents, and suggest the importance of SA for understanding the social functioning and close friendships of adolescents, especially girls.