Extraversion, a personality dimension associated with sociability, activity and dominance, predicts a man’s mating effort in various human populations. At a proximate level, individual differences in extraversion are likely to be mediated through testosterone, a strong hormonal correlate of men’s reproductive effort. However, the rare attempts to address this question have all been conducted in populations with low-fertility schedules, thus limiting the generality of the results. Using demographic, questionnaire and hormonal data from a high-fertility polygynous human population of Senegal, we first show that extraversion, a personality dimension predicting men’s mating behavior in this population, is associated with inter-individual differences in testosterone profiles, with men in the top quartile of extraversion distribution having 29% higher testosterone levels. We then show that personality profiles for neuroticism, openness and agreeableness are independent from testosterone levels. Since extraversion is the only personality dimension predicting men’s mating and reproductive success in this population, we suggest that variation in testosterone levels is primarily relevant for personality traits related to reproductive effort. The results have further implications to discuss possible evolutionary scenarios for the maintenance of variation in personality traits.