The findings of the literature on the predictive power of the Big Five personality model on academic and training success, vary to a large extent, according to several researchers. One of the reasons for the diverging conclusions may be attributed to cultural factors. This study makes an attempt to close this research gap as far as Greece is concerned, where there appears to be no such published study, involving university students. The purpose of the study is to close this gap, and offer both academics and practitioners additional insight, in their decisions, concerning training and education issues such as admissions to college or graduate programs, or who is to be trained. The methodology used in this study, involves the collection of the responses from 962 university students from a population of about 3000, who completed a structured questionnaire, including the variables of the Big Five model and the Dependent Variables of student performance measured by the student Grade Point Average (GPA), and the GPA the student believed she/he deserved, as well as the percentage of the modules passed out of those required. The results were analyzed with the use of SPSS using confirmatory factor analysis and Regression analysis. In accordance with the findings of earlier studies on personality and performance (both academic and work) Academic Performance correlated with extraversion, conscientiousness and emotional stability. Also, Perceived Academic performance related to extraversion and conscientiousness. Finally, Academic performance according to percentage of modules passed was related to age, agreeableness and conscientiousness. There are serious implications for tertiary education administrations, who can select their prospective students based not only on their past (school) performance, but also on the additional information provided by the personality tests of the candidates, increasing thus the chance of their completing their studies in a timely fashion.