Parent-adolescent relationships are related to adolescents' disclosure and concealment, but these associations may represent between-family differences (e.g., families with more negative interactions have adolescents who disclose less) or within-family processes (e.g., when a family has more negative interactions, their adolescent discloses less). This study used cross-lagged panel modeling (CLPM) and random-intercept cross-lagged panel modeling (RI-CLPM) to separate these elements. U.S. adolescents (N = 214, M[subscript age] = 16.0, 52% female) reported on their disclosure, concealment, positive relationships, and negative interactions with mothers 3 times over a year. Consistent with prior research, adolescent disclosure was transactionally associated with more positive and less negative relationships with mothers over time in between-family (CLPM) analyses. However, in the within-family (RI-CLPM) analyses, which controlled for the fact that more positive and less negative families had adolescents who disclosed more, changes in relationship quality within a family were not linked with changes in disclosure. In contrast, negative interactions and greater concealment were reciprocally related over time both between families and within families, even when considering that families with more negative interactions also had adolescents who concealed more. Positive relationships were associated with less adolescent concealment, but only relative to other families (at the between level) and not over time. Results confirm the importance of examining disclosure and concealment as separate processes, particularly at the within-family level, and indicate that the cycle of concealment and negative interactions among troubled families may be a particularly ripe area for intervention.