Introduction: Although a large part of the population may be exposed to various pressures that can lead to mental or eating problems and increased perceived stress, the transition from adolescence to adulthood has been shown to be a crucial stage. Medical students are particularly vulnerable during the transition period as they must adapt to new circumstances, which may contribute to increased perceived stress. Cortisol plays an important role between stress, weight gain, and the development of obesity. We designed a study to investigate the association between stress, eating behaviour, cortisol, and body weight in a sample of firstyear medical students. Methods: We determined 75 first-year medical students? hair and salivary cortisol concentrations by ELISA and related it to self-reported stress, eating behaviour, and anthropometric measurements throughout the academic period. The prevalence of overweight and obesity in females was 25% and 10%, and in males was 35% and 6%, respectively. We report an increase in hair cortisol, higher self-reported stress scores, and BMI mainly in females. Finally, we found evidence of positive associations between hair cortisol and BMI in females (r 5 0.348) and males (r 5 0.423). Conclusion: There is a low association between short-term single-point cortisol measures and long-term cortisol, mainly in males. Hence, short-term cortisol reactivity is moderately associated with long-term cortisol reactivity when both are evaluated simultaneously. These results support the previous evidence of positive associations between cortisol with body fat percentage and BMI, and finally, that eating behaviours are modified by academic stress perception, mainly in females.  Kulcsszavak: cortisol, stress, overweight, BMI, students