Background: Testosterone has been postulated as a 'social' hormone, but the relationship between testosterone and personality traits linked with socially oriented behaviors such as extraversion remains unclear. The objective of our study was to investigate the association between baseline salivary testosterone levels and the Big Five personality traits. Methods: We studied the relationship between salivary testosterone (morning and evening) and NEO-FFI (Five-Factor Inventory) personality traits in 1,611 participants with lifetime or current depression and/or anxiety and 482 participants without depression/anxiety of the Netherlands Study of Depression and Anxiety (NESDA). Results: The personality domain of extraversion was independently associated with higher salivary testosterone, both in healthy subjects (β = 0.094; p = 0.04) and in subjects with lifetime or current depression and/or anxiety (β = 0.092; p < 0.001). In multivariable adjusted analyses, extraversion remained the only personality trait that was positively associated with salivary testosterone (β = 0.079; p = 0.006). Conclusion: We conclude that salivary testosterone is consistently and positively related to extraversion, supporting the notion of a hormonal basis of this personality trait, which may be linked to the tendency to strive for and maintain social status.