Academic education poses a great challenge to students, whom are expected to work continuously and their final knowledge is evaluated by their exam grades. Due to high expectation during the study, some students use cognitive strategies such as defensive pessimism by setting low expectations in order to reduce the feeling of anxiety. In addition, some students are more likely to strive for higher achievements. In other words, they belong to a group of perfectionists. For instance, adaptive perfectionists want to reach the best possible academic achievement and to stand out, when compared to their fellow students. However, maladaptive perfectionism was often found to be correlated with worse academic achievement. All beforehand mentioned was often correlated with life satisfaction and flourishing as components of students' wellbeing. High adaptive perfectionist students show higher level of wellbeing, while high maladaptive perfectionists have shown lower levels of wellbeing. Therefore, the main aim of this study was to examine the contribution of perfectionism and defensive pessimism to academic achievement and components of wellbeing. 304 students from different universities in Croatia participated in an online study. Participants filled out Almost Perfect Scale–Revised, Defensive Pessimism Questionnaire, Short Form Satisfaction With Life Scale and Flourishing Scale. The most important positive predictor of defensive pessimism was the dimension of discrepancy (maladaptive perfectionism), followed by order and high standards (adaptive perfectionism), while age turned out to be negative predictor. Significant positive predictors of academic achievement were dimension of high standards, followed by sex and year of studying. Defensive pessimism was not significant predictor in explaining academic achievement. The most important significant negative predictor of life satisfaction and flourishing as components of wellbeing was the dimension of discrepany, while high standards and order were positive predictors. There was no predictive value of defensive pessimism in explaining the components of wellbeing.