Though differences in informant perceptions of family processes are associated with poorer health, few studies have examined discrepancies between father- and adolescent-report of family phenomena and their impact on adolescent mental health. This study examined how father and adolescent-reported parenting and the differences in their perceptions is related to adolescent mental health. Participants were 326 father–adolescent dyads (Fathers: Mage = 41.2; Adolescents: 7th grade students, Mage = 12.0, 48.5% female). Overall, analyses revealed significant main effects of father and/or adolescent report of father–adolescent conflict and harsh parenting on adolescent internalizing and externalizing symptoms. Analyses revealed two instances in which discrepancies between father- and adolescent-report of family phenomena was related to adolescent mental health. Given the mixed nature of the findings based on the outcome reporter, the current study discusses implications for discrepancy research and future directions to better understand discrepant perceptions as useful information on their own. The parent clinical trial is registered at ClinicalTrials.gov (Identifier: NCT03125291, Registration date: 4/13/2017).