Two studies investigated associations between family instability (changes in parents' intimate partners, work hours, residence, children's schools) and adolescent adjustment. In Study 1 (N = 141, M age = 15.23 years), instability was associated with increased caregiver-reported externalizing and internalizing behaviors (including youth-reported cigarette use), reduced teacher-reported frustration tolerance, social skills, task orientation, and lower academic grades. Logistic regression results for instability exposure showed an increased risk for school suspensions, Person in Need of Supervision status, binge drinking, and marijuana use. In Study 2 (N = 225, M age = 13.37 years), instability was linked to adolescent-reported externalizing and internalizing behaviors, teacher-reported disruptions, and lower English and math grades. Key sociodemographic factors and negative life events were statistically controlled in regression analyses. Results indicate that a more theoretically coherent measure of family instability, which is distinct from negative life events, may prove valuable in understanding the potentially adverse influence of instability on youth. (Contains 7 tables.)