A large literature base convincingly suggests that maternal and child characteristics interact to predict parenting practices and children’s emotional development. However, the independent and interactive effects of parent- and youth-level risk factors on emotion parenting behaviors and adolescent emotion lability over time is largely unknown. Using secondary data analyses of a longitudinal community sample of adolescents and their caregivers (N = 277), the current study examined the extent to which supportive vs. harsh parenting reactions to adolescents’ expressions of negative emotions underlie the longitudinal association between maternal emotion dysregulation and changes in adolescent emotion lability, and whether youth ADHD symptoms and sex impact these processes. Using structural equation modeling, results showed that mothers who reported being more emotionally dysregulated were more likely to endorse engaging in harsh parenting for boys with more ADHD symptoms, relative to mothers of adolescent girls or adolescents with fewer ADHD symptoms. Contrary to hypotheses, no other pathways were statistically significant. These results partially align with a transactional model of parenting wherein parent- and adolescent-level risk factors interact to confer risk for maladaptive parenting. Future work should further attempt to characterize the independent and interactive effects of maternal emotion dysregulation and youth ADHD symptoms on parenting and adolescent outcomes over time.