Motivation/problem statement: Medical students are among the brightest of students high and students are admitted selectively based on past academic performance. However with the failure rate in medical school, factors other than intelligence may be affect academic performance. Contrary to the traditional belief that stressful experiences are necessary for future medical practice, research suggests that stress and anxiety are major causes of cognitive dysfunction ( Vitaliano, 1984). . Dyrbye et al.,(2006) in a systematic review reported that there are limited data available regarding the causes of student distress and its impact on academic performance, dropout rates, and professional development. The aim of this study was to determine factors that affect performance in Physiology Part 1 examination among Medical and Dental students at the University of Ibadan, Nigeria. Methods: Semi structured self administered questionnaire was used. The questionnaire contained questions on sociodemographic data. Perceived Stress Scale developed by Cohen and Mermeistein in 1983 was used. . Subjects were grouped as stressed or not stressed. Hospital anxiety and depression scale was used to collect data on psychological distress. Scores in Physiology examination was obtained from Departmental records. Results: Of the 130 questionnaires that were filled, examination results were obtained for 100 students, who provided student identification numbers. Factors affecting performance in Physiology – There was no association between gender and success in physiology (p=0.42). The mean age of those who passed (20.44±2.58 years) was lower than the mean age of those who failed (22.55±5.13 years) There was statistically significant association between age and performance (p=0.028). A higher proportion of medical students (93.7%) passed compared with dental students (71.4%) (p=0.004). There was statistically significant association between Cumulative GPA groups in first year and success in Physiology examination,. (p=0.003). Association between stress and psychological distress and performance in Physiology (Figure 3) Among those who failed, 72.7% had perceived stress compared with 27.3% who did not perceive stress ( p=0.001). There was a statistically significant association between anxiety and performance in physiology. A higher proportion of those who failed were anxious (60%) compared to those who were not anxious (40%) (p=0.042). There was no association statistically significant association between depression and success in Physiology (p=0.173) Conclusion. Anxiety and perceived stress were associated with poorer performance, however depression did not affect performance among the students. Further research needs to be done to determine source of stress and anxiety. Preventive measures need to be put in place to enhance performance.