Purpose: There is evidence that traditional gender-role attitudes are associated with poor mental health outcomes in adults; however, few studies have examined associations among adolescents. We sought to test associations between gender-role attitudes and mental health among Australian adolescents. Methods: Data were drawn from the Longitudinal Study of Australian Children, a nationally representative Australian study. Participants were 3,059 adolescents with complete data for Waves 5-6 (years 2012-2014, aged 12/13 and 14/15 years). Analyses were stratified by sex and controlled for parental education, household income, area socioeconomic position, ethnicity, religiousness, and household type. Multivariable linear regression analyses were conducted to test associations. Results: Egalitarian gender-role attitudes were associated with fewer conduct problems for adolescent males (beta-.04, 95% confidence interval [CI] -.08 to .00; p = .048) and females (beta-.06, 95% CI -.11 to -.01; p = .014), and for females, less hyperactivity (beta-.15, 95% CI -.20 to -.09; p < .001), better prosocial behavior (beta.08, 95% CI .03 to .13; p = .003), and better overall mental health (beta-.27, 95% CI -.43 to -.11, p = .001). There were no associations for peer problems or emotional problems. Associations were more apparent for females than for males, and analyses using adolescent- and teacher-reported mental health supported the main findings. Conclusions: Egalitarian gender-role attitudes among adolescents are associated with better outcomes on some dimensions of adolescent mental health, suggesting that establishing egalitarian gender attitudes in adolescence could help impart mental health benefits among this population group. (C) 2019 Society for Adolescent Health and Medicine. All rights reserved.