Although sleep has been linked to changes in positive and negative affect across the lifespan, the prediction of sleep from affect has not been explored completely. As such, the main objective of this study was to examine the association between affect and sleep across the adult lifespan, using a novel gauge of affect, the positivity ratio. Both subjective and objective assessments of sleep were used in analyses. This study was an archival analysis of data collected as a part of the Midlife in the United States Study (MIDUS-II), with participants ranging from 34 to 83 years of age. Results revealed the positivity ratio to be a significant predictor of self-reported sleep quality and global sleep, but not of objective sleep measures. Additionally, the positivity ratio was found to increase with age and appears to predict better global sleep and sleep quality across all age groups. Implications of the findings are discussed.