Affective temperaments have been shown to robustly affect infertility treatment success. However, identification of possible mediating factors through which they exert their influence is still lacking. A growing number of results suggest that adherence to recommended treatments may be such a mediator, on the one hand, because affective temperaments are known to influence adherence and, on the other hand, because non-adherence negatively influences the treatment outcome. Recommended treatment of infertility involves, beyond medications, dietary and lifestyle changes. The aim of this retrospective cohort study was to evaluate whether adherence to physician-prescribed diet and physical activity recommendations mediates the effect of affective temperaments on infertility treatment outcomes. Among 308 women who underwent infertility treatment in an Assisted Reproduction Center, affective temperaments, adherence to diet, adherence to physical exercise, and infertility treatment success (clinical pregnancy) were assessed besides detailed medical history and demographic parameters. Associations between affective temperaments, adherence to diet and recommended physical activity, and assisted reproduction outcomes were analyzed using generalized linear models and causal mediation analysis. Adherence to physical activity didn't have an effect, but diet adherence increased the odds of infertility treatment success by 130% suggesting its role as a potential mediator. Based on causal mediation analysis, higher depressive and anxious temperament scores were directly associated with 63% and 45% lower odds of achieving clinical pregnancy, respectively, with effects not mediated by diet adherence. Higher irritable temperament scores indirectly decreased the odds of achieving clinical pregnancy by 14%, mediated by diet adherence; while higher cyclothymic temperament scores decreased the odds of achieving clinical pregnancy both directly by 51% and indirectly, mediated by diet adherence by 11%. Our results suggest that diet adherence mediates the mechanism by which irritable and cyclothymic affective temperaments influence IVF treatment success. Since adherence is a modifiable risk factor of infertility treatment success, screening for affective temperaments may help to identify potentially high-risk non-adherent patient groups and offer patient-tailored treatment, which may help increase the chances of a successful pregnancy and live birth in women undergoing IVF treatment.