Family instability and involvement in interparental conflict have long been identified as risk factors for adolescent depression; however, adolescent perceptions may be an underexamined measure of family instability which could produce cascading effects toward depressive symptoms. Altered perceptions due to cognitive maturation and puberty may make adolescents particularly attuned to deviations in the stability of the family system. Moreover, their involvement in parents’ conflicts may further amplify their vulnerability to these stressful environmental experiences and increase their likelihood of depression. Therefore, perceived family instability, involvement in interparental conflict, and depressive symptoms were examined in 296 adolescents (50.3% female, mostly White) across three annual waves starting at age 13 years. Using autoregressive latent trajectory modeling, between-person results showed that adolescents with higher initial levels of perceived family instability tended to show higher initial depression levels, and some adolescents’ involvement in their parents’ disputes increased faster than others over this three-year period. Within-person results indicated that adolescents experiencing higher-than-usual perceived family instability at age 14 exhibited significantly higher depressive symptoms at age 15, pointing to the unfolding emotional cost of instability for early-to-middle adolescents. Findings emphasize modeling enduring vulnerabilities and intra-individual fluctuations in family and emotional processes during adolescence.