Objective: The current study examines associations between five factor personality traits and average sleep duration, sleep deficiency, and sleep problems. Method: The participants were from two population-based samples from Australia (n = 1,104, age range 31-41) and Finland (n = 1,623, age range 30-45). Self-reports of sleep behavior, sleep problems (Jenkin's scale), and five factor model personality traits (NEO-FFI) were collected. Associations between personality traits and sleep were analyzed with linear regressions. Results: The results showed that higher extraversion, agreeableness, and conscientiousness were, in general, associated with better sleep, whereas higher neuroticism was associated with sleeping less well. Openness was not associated with sleep. Most of the associations were replicable between the samples from the two countries, but personality traits explained only small part of the variance in sleep behavior. Conclusions: Increasing the knowledge on personality and sleep may benefit more personalized treatment of sleep disorders and help in personnel selection to jobs in which it is critical to stay alert. However, longitudinal research is needed to confirm the current findings. (PsycINFO Database Record © 2014 APA, all rights reserved).