This study evaluated the Social Anxiety Scale for Adolescents (SAS-A) as a modified version of the Social Anxiety Scale for Children—Revised (SASC-R) for use with adolescents. It examined the relationship between adolescents' social anxiety (SA) and their peer relations, friendships, and social functioning. Boys (n = 101) and girls (n = 149) in grades 10–12 completed the SAS-A and measures of social support, perceived competence, and the number and quality of their best friendships. Factor analysis 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 higher levels of SA than boys, and SA was more strongly linked to girls' social functioning. Adolescents with higher SA reported poorer social functioning, including less support from classmates and less social acceptance. Girls with higher SA reported fewer friendships and less intimacy, companionship, and support in their close friendships. These findings extend the SASC-R to adolescents and highlight the importance of SA in understanding adolescents' social functioning and friendships, especially for girls. Social anxiety is critical for understanding adolescents' interpersonal functioning, as peer relationships are essential for developing social skills and personal competence. The study also aimed to evaluate gender differences in SA and linkages between SA and peer relationships. The results suggest that girls are more vulnerable to social anxiety, which may affect their social functioning. The study also evaluated the SAS-A's factor structure and psychometric properties, aiming to provide a tool for assessing social anxiety across a broad age range. The findings have implications for understanding the onset and course of anxiety disorders, such as social phobia, and for developmental and clinical research.This study evaluated the Social Anxiety Scale for Adolescents (SAS-A) as a modified version of the Social Anxiety Scale for Children—Revised (SASC-R) for use with adolescents. It examined the relationship between adolescents' social anxiety (SA) and their peer relations, friendships, and social functioning. Boys (n = 101) and girls (n = 149) in grades 10–12 completed the SAS-A and measures of social support, perceived competence, and the number and quality of their best friendships. Factor analysis 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 higher levels of SA than boys, and SA was more strongly linked to girls' social functioning. Adolescents with higher SA reported poorer social functioning, including less support from classmates and less social acceptance. Girls with higher SA reported fewer friendships and less intimacy, companionship, and support in their close friendships. These findings extend the SASC-R to adolescents and highlight the importance of SA in understanding adolescents' social functioning and friendships, especially for girls. Social anxiety is critical for understanding adolescents' interpersonal functioning, as peer relationships are essential for developing social skills and personal competence. The study also aimed to evaluate gender differences in SA and linkages between SA and peer relationships. The results suggest that girls are more vulnerable to social anxiety, which may affect their social functioning. The study also evaluated the SAS-A's factor structure and psychometric properties, aiming to provide a tool for assessing social anxiety across a broad age range. The findings have implications for understanding the onset and course of anxiety disorders, such as social phobia, and for developmental and clinical research.