Background: Leisure-time sitting-time (LTST) is seen as a possible independent risk-factor for physical and mental health, but research on psychological determinants is sparse. Associations between sitting-time and the personality dimensions of neuroticism, extroversion, openness, agreeableness, and conscientiousness, and the role of general self-efficacy (GSE) were investigated. Methods: A population-based, cross-sectional study was conducted at the Research Centre for Prevention and Health, Denmark, in 2006-08. Men and women (N = 3471) aged 18 to 69, were randomly sampled in the suburbs of Copenhagen. The NEO Five-Factor Inventory, the General Self-Efficacy-Scale, and the Physical Activity Scale 2 were used. Results: Negative associations were found between LTST and extroversion, conscientiousness, and openness, while neuroticism showed a positive association (R-2 = .13). The associations with agreeableness became significantly positive, when GSE was included. All 5 associations were mediated by GSE, with mediation proportions between 23%-60%; but with modest effect sizes. Conclusions: These cross-sectional results indicate that personality traits and GSE could be considered as associates of LTST; but future longitudinal data are necessary to make causal statements and rule out alternative models fitting data.