The majority of research investigating the social functioning of youth with ADHD has examined peer rejection and social skills deficits while generally overlooking their friendships. The goal of this dissertation was to provide detailed information about friendship quality in adolescents with and without ADHD. The first manuscript compared ratings of social support and negative interactions in same- and other-sex friendship dyads in adolescents with and without ADHD, while examining the potentially moderating effects of age and gender. The second manuscript examined empirically supported correlates of friendship quality including friendship stability, co-morbid psychopathology, and interpersonal competence. A sample of 115 adolescents, ages 13-18, were recruited to participate in the present study of whom 61 were classified as having ADHD (21 female) and 54 without ADHD (29 female). The measures used included parent and self-report rating scales and questionnaires assessing ADHD symptoms, friendship quality, friendship stability, externalizing behaviour (conduct problems, oppositional behaviour), internalizing behaviour (anxiety, depression), and interpersonal competence (social skills, social perspective taking). Results from study one indicated that ratings of friendship social support diminished across age groups in youth with ADHD, but increased in typically developing youth. Adolescents with and without ADHD, however, did not differ on ratings of negative interactions experienced in their friendships. Compared to males, females rated their friendships to be more supportive, irrespective of ADHD status. Adolescents with and without ADHD rated their same-sex friendships to be simultaneously more supportive and more conflictual than their other-sex friendships. Results from study two indicated that friendship stability, social skills, social perspective-taking, oppositional behaviour, and anxiety explained unique variance in the prediction of friendship social support. However, results of exploratory mediation analyses indicated that the direct effects of oppositional behaviour and anxiety were no longer significantly predictive of friendship quality, after controlling for the mediators social skills and social perspective-taking, respectively. These findings, clinical implications, and future directions are discussed within the context of the existing peer relations literature.