Objective: Sleep is vital for healthy development, yet most adolescents do not meet recommended nightly hours. Although racial/ethnic minorities often experience relatively worse sleep outcomes compared with White peers, little is known about how the sleep-mental health relationship holds across diverse groups or how family relationships affect this association. Method: Using data on 8th, 9th, and 11th grade public school respondents to the 2016 Minnesota Student Survey (N = 113,834), we conducted univariate, bivariate, and multivariate analyses to examine whether sleep duration was associated with depressive symptoms, suicide ideation, and suicide attempt, adjusting for sociodemographic covariates. Furthermore, we examined the effect of the parent-child connectedness by sleep interaction on these relationships. Analyses were conducted for 9 racial/ethnic groups collectively and separately. Results: Overall, youth sleep duration and parent-child connectedness were independently associated with reduced rates of depressive symptoms, suicide ideation, and suicide attempt. There was significant interaction between parent-child connectedness and sleep, demonstrating that connectedness magnifies the benefits of the sleep-mental health relationship. Main effects of sleep and parent-child connectedness for mental health were similar for most individual racial/ethnic groups, although magnitudes varied. The connectedness-sleep interaction only remained significant for White and Asian youth on select suicide-related outcomes. Conclusion: Despite racial/ethnic differences, adolescent sleep and parent-child connectedness both seem to buffer youth from poor mental health in a large, multiethnic sample. On the whole, these factors demonstrate a synergistic protective effect and reflect promising intervention targets. The extent to which their interactive benefit translates across diverse populations requires additional study. [This is the online version of an article published in "Journal of Developmental and Behavioral Pediatrics."]