The purpose of the current study was to investigate the dynamic process of disclosure within the adolescent–mother relationship by examining how maternal personal distress and validation of adolescent negative affect would be related to adolescent disclosure of a distressing experience for the first time. A community sample of 66 mothers and their adolescent children (M = 14.31 years, 58% female) participated. The adolescents disclosed an emotionally distressing experience to their mothers for the first time. Mothers’ validating behaviors and personal distress in response to their adolescents’ expressions of negative emotion were predictive of adolescent disclosure. Adolescents made less detailed or substantive disclosures to their mothers when adolescents perceived their mothers as less validating of their negative emotions and when mothers were more likely to become distressed themselves. Neither adolescent-perceived maternal invalidation nor observed maternal validating or invalidating behaviors were related to adolescent disclosure. Maternal personal distress was further indirectly associated with less substantive disclosures through less maternal validation of negative emotion. These findings provide the foundation for future research evaluating clinical interventions targeted at increasing mothers’ emotion regulation skills and validation of children’s negative emotions. Such interventions may provide an effective way to promote better mother–adolescent communication, especially in regard to distressing experiences.