This study uses a longitudinal design to investigate the effects of online dating sites on first date success. Participants were surveyed before their first date with someone from an online dating site (N = 186) and again after meeting their partner in person (N = 94). As part of the survey, they also supplied the e‐mails they had sent to their partner through the dating site so their actual communication could be examined. Findings indicated that first date success was predictable from features of participants' online impressions and relational dynamics. The results are discussed in terms of their theoretical and methodological contributions to the literature on relationship development, as well as their practical implications for online dating sites and users.