Background: Approximately 1 in 10 fathers of infants experience symptoms of common mental health disorders, prompting calls for paternal postpartum screening. However, numerous obstacles exist to screening implementation. The aim of this study was to provide preliminary evidence for an alternative approach that starts with asking fathers about their sleep. Methods: Using self-reported father data at 0 to 36 months postpartum (N=1204) from four Australian cohort studies, we assessed associations between responses to various single-item questions about sleep (good to poor), and scores on validated measures of mental health (depression, anxiety and stress). We conducted regressions, unadjusted and adjusted for father age, child age, household income, education, first or later child, and marital status, to test associations between sleep and each indicator of mental health. We then meta-analyzed effects and assessed interactions between sleep and each of the covariates. Results: Consistent associations between fathers’ subjective poor sleep and depression, anxiety and stress were replicated across the four cohorts despite heterogeneity in the sleep questions. At the meta-analytic level, effects ranged from weak to moderate (0.25 to 0.37) and were robust to all adjustments. Interactions were only detected between family income and poor sleep, such that the association was stronger for high income fathers. Limitations: This study does not address the sensitivity or specificity of single-item sleep questions for assessing paternal mental health risk. Conclusions: A low-cost, non-stigmatizing single question to postpartum fathers about their sleep may present a gateway opportunity to enquiring about mental health.