This study was undertaken to measure the prevalence of psychological morbidity, and the nature and source of stress, in first year medical students. Two hundred and four first year medical students at a university in the north of England were sent a postal, self-report questionnaire. They were asked to complete the General Health Questionnaire (GHQ), the Stress Incident Record and to give details of their alcohol consumption. A total of 172 students (84.3%) replied. Thirty-six per cent of the students scored above the threshold of the GHQ, indicating probable psychological disturbance. There was no difference between men and women. Approximately half of the students described a stressful incident, the majority of which were related to medical training rather than to personal problems. Male students reported drinking significantly more alcohol than female students, but there was no relationship between levels of alcohol consumption and either psychological disturbance or reporting of stress. The findings suggest that even at the preliminary stages of medical training, many students find aspects of the medical course very stressful. The psychological well-being of medical students needs to be more carefully addressed, and closer attention paid to the styles of medical teaching that may provoke avoidable distress.