Objective: to investigate whether personality types predict medical school stress.Setting: all four medical schools in Norway.Participants: 236 medical students, mean age 21.7 ± 2.6 years (SD).Main outcome measures One month after medical school started, each student s personality was typed by combining high and low scores of three personality traits: extroversion (E), neuroticism (N), and obsessiveness (O). This method categorised the students into the following personality types: spectator, insecure type, sceptic, brooder, hedonist, impulsive type, entrepreneur, and complicated type. The relationships between each of the resulting eight personality types and perceived medical school stress were assessed at mid-curriculum (T2) and in the final term (T3).Results Predictor analyses in which personality types were adjusted for age and gender showed that hedonists were protected against medical school stress at both T2 (beta = 0.17, P = 0.01) and T3 (beta = 0.21, P = 0.002). The complicated types (beta = 0.15, P = 0.03), and the brooders (beta = 0.15, P = 0.02) were at risk of experiencing high medical school stress at T3.Conclusions This is the first study to show that a specific combination of personality traits can predict medical school stress. Hedonists, who are low in both neuroticism and obsessiveness, are protected against medical school stress. Conversely, brooders and complicated types, who are high in both traits, are at risk of perceiving high levels of medical school stress nearly six years later.