Background: Stress caused by the high physical, intellectual and emotional demands imposed to medical students, renders them specially susceptible to the development of mental disorders. Aim: To assess the prevalence of risk for mental disorders among undergraduate students at the Medical School of the Catholic University of Chile. Material and methods: The Twelve Item General Health Questionnaire (GHQ 12) was voluntarily answered by medical students from the first to the fifth year. Results: Sixty eight percent of the total population (305 students) answered the questionnaire. Forty one percent of students were at risk, defined as scoring five or more points in the GHQ 12. The average score was 3.9±2.2. First year students had a higher score than fourth year students (4.6±2.2 and 3.4±2.1 points respectively, p <0.05). No gender differences were observed. Conclusions: Our results are similar to those of other publications concerning psychiatric risk among medical students (Rev Méd Chile 2001; 129: 173-78).