Medical students are subject to stress from sources related to medical training in addition to personal problems, resulting in significant mental distress. This study evaluates the scope of the problem in Tehran medical schools and sheds light on some of its associations. Students (604) of medicine from four medical schools in the city of Tehran responded to the Persian version of 28-item General Health Questionnaire (GHQ-28) in conjunction with a data collection sheet asking about age, sex, marital status, current training level, living place, grade point average in previous semester, and perceptions of their financial status. Of 602 students, 40.7% had mental distress (45.7% of female and 36.7% of male students). Distress was associated with being a woman (female to male odds ratio: 1.55) and very poor financial status (OR: 18.0).