This research study aimed to generate a substantive theory of mothers’ and adolescent daughters’ experiences of disclosing and not disclosing about their lives within the context of their relationships. Thirty biologically related mothers and adolescent daughters (15 mothers, 15 adolescent daughters) were separately interviewed using an in-depth, semi-structured interview guide. Mothers’ mean age was 44.8 years and adolescent daughters’ mean age was 14.13. Both data collection and analysis were guided by a constructivist grounded theory methodology (Charmaz, 2006) and carried out by the researcher. The results of the analysis indicated three categories that capture mothers’ and adolescent daughters’ experiences of disclosing and not disclosing: (a) context of disclosing and not disclosing, which refers to mothers’ and adolescent daughters’ explanations of what, where, how, and when they were disclosing and not disclosing, (b) relational influences, which includes the ways in which the mother-adolescent relationship was talked about as shaping both disclosures and non-disclosures, and (c) the process of disclosing and not disclosing, which encompasses mothers’ and adolescent daughters’ interactional processes of disclosing and not disclosing. A preliminary theory of mothers’ and adolescent daughters’ experiences of disclosing and not disclosing within the context of their relationships was developed based on these three categories. This substantive theory positions mothers’ and adolescent daughters’ disclosures and non-disclosures as dyadic processes shaped by relational attunement, relational quality, and relational norms, in addition to being contextualized by topics, locations, means, and timing. These analytic findings also indicate that disclosure and non-disclosure processes are reflective of the mother-adolescent daughter relationship, while the mother-adolescent daughter relationship is reflective of disclose and non-disclosure processes. This substantive theory extends and supports existing research in the area of disclosure and non-disclosure in parent-adolescent relationships. This study is the first to provide a theoretical conceptualization of mothers’ and adolescent daughters’ experiences of disclosure and non-disclosure. Moreover, whereas published research has exemplified a heavy causal orientation by identifying predictors, outcomes, and correlates of disclosure and non-disclosure in parent-adolescent relationships, this study explicitly focuses on understanding disclosure and non-disclosure processes between mothers and their adolescent daughters.