The medical course has always been regarded as highly stressful. Excessive stress causes physical and mental health problems. Persistent stress will impair students'' academic achievement, personal and professional development. Early detection and prevention of this condition will help in reducing the negative impacts of stress on medical students. The purpose of this study is to explore the nature of stress among medical students by determining the prevalence, sources, pattern, and determinant factors of stress. It is hoped that understanding the nature of stress will help medical teachers find ways to reduce and minimize the stress level of medical students during their study. A cross-sectional study was done on all medical students in the university. The prevalence of stress among medical students in USM is high. Academic related problems were the major stressors among medical students. Year of study was the factor most significantly associated with medical students'' stress level. There was bimodal pattern of stress level throughout the year of study, peaking at the second and fourth years of study.