Poor sleep has been linked to behavioral and emotional changes, impairments in cognitive functioning, and daytime dysfunction. Positive affective experiences may serve as a potential factor in promoting healthier sleep. Prior research has linked sleep to changes in both positive and negative affect across the lifespan, but the prediction of sleep from affect has not been extensively studied. Accordingly, we examined the association between affect and sleep across the adult lifespan, using a novel gauge of affect, the positivity ratio. The positivity ratio is a measure of how much positive affect an individual has in relation to his or her negative affect. We also explored age as a potential moderator between the positivity ratio and sleep outcomes. The study was an archival analysis of Midlife in the United States study (MIDUS-II) data. Participants (N = 1,172, 34–83 years old) completed the MIDUS-II PANAS, from which positivity ratio scores were derived. Sleep was assessed through the Pittsburgh Sleep Quality Index, actigraphy, and daily global sleep diaries. Hierarchical linear regressions were performed to predict sleep from affect. The moderation was tested using Hayes’ SPSS PROCESS macro. Higher positivity ratios significantly predicted better self-reported daily sleep quality (β = -.187, p = .001) and higher Global Sleep Scores (β = -.937, p < .001), but not objective sleep measures. Even with negative affect present in the positivity ratio, higher positivity ratios predicted better sleep, indicating that positive affect may serve a protective function. Positivity ratios increased with age (β = .017, p < .001) and predicted better global sleep and sleep quality across adulthood. These findings extend existing research on sleep and affect by providing an examination of how affect, positive and negative concomitantly considered, predicts sleep. This study provides evidence for the positivity ratio and subjectively-rated sleep quality association, extending prior literature linking the positivity ratio to subsequent health outcomes. Given that the positivity ratio is an equal predictor of sleep across the lifespan, clinicians should examine emotional regulation in addition to cognitive and behavioral components in sleep interventions. N/A