Limited involvement of youth with developmental disabilities (DD) in mentoring programs has resulted in limited knowledge about the quality and impact of these relationships. The self-disclosure process has been identified as one factor impacting relationship development (Reis & Shaver, 1988). We proposed a theoretical model to examine the role of the self-disclosure process as a mechanism in peer mentoring relationship development for transition-age youth with DD by determining if selfdisclosure occurred, the type of information shared, how peer mentors responded, and if the process differed by perceived relationship quality. This retrospective, observational study purposefully selected nine peer mentoring dyads from a problem-solving intervention with a peer mentoring component to examine relationships judged by the researchers, peer mentors, and peer mentor supporters to be of variable quality (strong, moderate, weak), including 9 youth and 5 peer mentors with DD. Peer mentoring included 8 structured calls each with specific objectives. Phone call recordings were coded and dyads were grouped by perceived quality to determine how the self-disclosure process differed by relationship quality. The findings indicated self-disclosure occurred in each relationship at high rates (59%) and peer mentors responded to almost all selfdisclosures (98%). A higher quantity of self-disclosure and more frequent disclosure of vi emotions were found in relationships of higher quality. Peer mentors in higher quality relationships more frequently responded to self-disclosure with advice or their own selfdisclosure. Implications of findings and use of the self-disclosure process as a mechanism for promoting high quality peer mentoring relationships are discussed.