OBJECTIVE: The present study examined the longitudinal association between personality traits and sleep quality in 4 samples of middle-aged and older adults. METHOD: Participants (N > 22,000) were adults aged 30 to 107 years old from the Wisconsin Longitudinal Study (WLS), the Midlife in the United States Study (MIDUS), the Health and Retirement Study (HRS), and the Midlife in Japan Study (MIDJA). Personality and sleep quality were assessed at baseline and again 4 to 10 years later. RESULTS: Scoring lower on neuroticism and higher on extraversion was associated with better sleep quality at baseline and over time, with effect sizes larger than those of demographic factors. Low conscientiousness was associated with a worsening of sleep quality over time. Openness and agreeableness were unrelated to sleep quality. Poor sleep quality at baseline was associated with steeper declines in extraversion, agreeableness, and conscientiousness and a smaller decrease in neuroticism over time. CONCLUSION: Replicable findings across samples support longitudinal associations between personality and sleep quality. This study identified specific personality traits that are associated with poor and worsening sleep quality, and substantiated previous findings that poor sleep quality is associated with detrimental personality trajectories. (PsycINFO Database Record