Online dating sites (ODSs) have become popular with users trying to find partners. The purpose of this study was to determine the role that biological and personality traits play in the use of online dating websites. A cross sectional survey with 678 participants—including cohorts from college as well as the general population—provided data for this study. The Five Factor Model personality model (FFM), sexual orientation, and biological sex were utilized as antecedents to the uses of and gratifications from online dating sites. Results uncover sex and sexual orientation differences in both personality traits and gratifications sought from online dating sites. Specifically, women and homosexuals were found to be more neurotic, women were more agreeable, and homosexuals were more open to experiences. Homosexual users sought a wider range of gratifications (relationship, sex partner, distraction, and convenient companion) from online dating sites than their heterosexual counterparts. Women were less likely to use ODSs to find sexual partners, but more likely to use ODSs to be social. Those who were neurotic use dating sites to build an identity, as a convenient companion, and as a distraction. People who are open to experiences were found to use dating sites to be social. Disagreeable people use dating sites because of peer pressure and as a status symbol, and conscientious people were found to use dating sites to find a relationship.