Abstract Background and purpose: this research was conducted with the aim of predicting dangerous sexual behavior, deviant behavior and extramarital relationships of couples based on dark triads of personality. Methodology: this research is applied in terms of purpose and descriptive-correlation in terms of method. The sample of this research includes 247 couples who referred to Baran counseling clinic in the first 3 months of 2013 in Tehran. The data of this research have been collected using standard questionnaires. Cronbach's alpha method was also used to determine the reliability of the questionnaire. Finally, the hypotheses were tested using path analysis modeling and using AMOS version 22 software. Findings: the results of this research were based on the prediction of dangerous sexual behaviors, deviant behavior and extramarital relationships of couples based on the dark triads of personality. The findings of this research showed that three dark aspects of personality (Machiavellianism, narcissism and psychosis) had a positive effect on sexual risk behavior and deviant behaviors. The effect of Machiavellianism and psychosis on extramarital relationships was also positive (p<0.05) but the effect of narcissism on extramarital relationships was not significant (p>0.05).