Background: Reducing stigma associated with mental illness is an important aim of medical education, yet evidence indicates that medical students' attitudes toward patients with mental health problems deteriorate as they progress through medical school. Objectives: Authors examined medical students' attitudes to mental illness, as compared with attitudes toward other medical illness, and the influence of the number of years spent in medical school, as well as of several key socio-demographic, ethnic, and cultural variables. Methods: A group of 760 U.K. medical students completed a nationwide on-line survey examining their attitudes toward patients with five conditions (pneumonia, depression, psychotic symptoms, intravenous drug use, long-standing unexplained abdominal complaints), using the Medical Condition Regard Scale (MCRS). Students were also asked whether they had completed the psychiatry rotation or had personal experience of mental disorders themselves or among their friends or family members. They were also asked about their ethnic group (using U.K. national census categories), religious affiliation, and how important religion was in their lives. Independent-samples t-tests and one-way ANOVA were used to compare differences between groups on the MCRS. Results: Students showed the highest regard for patients with pneumonia and lowest regard for patients with long-standing, unexplained abdominal complaints. Although attitudes toward pneumonia were more positive in fifth-year students than in first-year students, attitudes toward unexplained chronic abdominal pain were worse in fifth-year students than in first-year students. Personal experience of mental health treatment, or that among family and friends, were associated with less stigmatizing attitudes. Men showed more stigmatization than women for nearly all conditions; Chinese and South Asian students showed more stigmatizing attitudes toward delusions and hallucinations than their white British counterparts. Conclusions: Medical students in this survey showed the lowest regard for patients with unexplained abdominal pain, and these attitudes were worse in the most experienced medical students. Students' gender, culture and direct or indirect experience of mental illness influenced stigmatizing attitudes. (Contains 4 tables and 1 figure.)