There is growing interest in examining dark personality traits, to better explain malevolent and self-serving behaviour patterns commonly observed in clinical and non-clinical settings. Recently, taxonomies of dark personalities have been developed, along with psychometric tools to measure and delineate between traits including psychopathy, Machiavellianism and narcissism. The extent to which these constructs are distinct or overlapping remains controversial. Psychophysiological research can improve understanding of biological mechanisms contributing to personality that may help to evaluate taxonomies. This study investigated diurnal variations (...) in salivary cortisol (on waking, cortisol awakening response, and at bedtime, over two days) and their relationship to personality traits (Short Dark Triad Scale and IPIP Mini), psychopathology (Depression, Anxiety and Stress Scale; DASS) and quality of life (WHOQOL-BREF) in a non-clinical sample (N=45, 26 females, 19 males, 18-59 years). Dark personality traits correlated with low bedtime cortisol, reduced sleep, depression and poorer quality of life. Hierarchical linear regressions analyses indicated that bedtime cortisol levels significantly accounted for variance in Psychopathy (F(1,39)=5.55, p=.02, R=.52, B=-1.81, 95% CI [-3.37-(-.26)], β=-.33, sr2=.10) and reduced sleep uniquely accounted for variance Machiavellianism (F(2,40)=5.99, p=.01, R=.48, B=1.01, 95% CI [.16-2.02], β=.34, sr2=.11). These data provide preliminary evidence that supports the cortisol hypoarousal hypothesis of Psychopathy and has identified a link between Machiavellianism, sleep-wake cycles, and chronotype. The hypoarousal hypothesis of Psychopathy contends that the hypothalamic-pituitary-adrenal axis is unresponsive to the stress of social engagement. Machiavellianism was predicted by longer days with evidence for an evening chronotype. These findings indicated that the Dark Triad traits have different underlying biological mechanisms that require further exploration. (shrink)