The medical profession plays a chief role in the health of a nation, thus the standard of training of its medical student is raised to reflect excellence. Determining factors that affect success in medical exams is essential in preventing academic failure, boosting the self-esteem of medical students and at a community level, it assures the production of better doctors and improvement of patients satisfaction. This study looked at the various socio-demographic factors, personal factors, familial factors and education factors and how they determine outcome of on success in professional exams in medicals students of the University of Nigeria. It was a descriptive cross-sectional study and the study population was selected using multistage sampling method. A total of 280 students participated in the study. The result was analyzed using the statistical package for social science version 23.3. The study found a statistical significant relationship between academic performance and gender (p = 0.015). Females (68.8%) passed more than males (54.4%). There was a gradual decrease in success rate as the students progressed in class (success rates of 400,500 and 600 level students were 76.1%, 57.3% and 49.5% respectively) with p = 0.001. A statistical significant relationship (p = 0.013) between academic performance and the number of hours participants spent on movies, series and music per day was noted. Not combining school and work was associated with a high success rate (63.4%) with p-value significant at 0.015. There is also a statistical significant relationship (p value = 0.001) between academic performance and having financial dependents. Parents low level of education, lack of parent-child relationship, low family income and conflict with family members are familial factors that affect success. Educational determinants include hectic class and posting schedule, unfriendly classroom environment, inappropriate teaching methods by lecturers, inadequate facilities and poor student- lecturer relationship. It was noted that students, families and stakeholders in education should all play a role in improving medical students success. There is a need to orient students on study styles and habit. Families should provide emotional support.  Programs to aid indigent students should be initiated and stakeholders should provide education friendly environment for learning.