Despite positive and negative emotions being equally important predictors of adolescent wellbeing, research examining positive emotions is limited. In 4582 adolescents (69.4% females; age M ± SD = 14.55 ± 1.74 years), we used structural equation modelling to examine associations between self-reported sleep duration and quality with positive affect, negative affect, and happiness, controlling for age and sex. Overall, sleep quality displayed stronger associations with all measures of emotions compared to sleep duration. Shorter sleep was more specifically associated with lower positive emotions (happiness, followed by positive affect), whereas poorer sleep showed stronger associations with negative affect. Protecting sleep duration may promote positive emotions and enhancing sleep quality may reduce mood disturbances. Future research could incorporate both positive and negative emotions to better understand adolescents' wellbeing.