Objective: This study aims to determine attitudes of medical students towards mental illness, the effective factors in their attitudes and to reveal their educational needs. Methods: This cross-sectional research consisted of qualitative and quantitative methods. The study group included 744 2nd year and 5th year students, 21 healthcare personnel and 10 faculty working in psychiatry clinic in Medical Schools at Ankara University and Akdeniz University. Sociodemographic information form, stigma scales (Characteristics Scale, Affective Reaction Scale, Social Distance Scale) for alcohol-substance abuse, schizophrenia and depression, focus group discussion and individual interview methods were used to collect data. Stigma scales were applied on medical students and healthcare personnel. Four focus group discussions were conducted with the 5th year students and semi-structured individual interviews were made with faculty. Results: It is observed that medical students have stigmatization tendency mostly to alcohol-substance abusewhich is followed by schizophrenia and depression, respectively. Characteristics Scale scores for alcohol-substance abuse and Social Distance Scale scores for schizophrenia of the 5th year students exhibit statistically less stigmatization than of the 2nd year students. According to the regression analysis, variables related to stigmatization are gender, economic status of family, presence of mental illness in family, education period and having mental illness. Qualitative data indicated that being diagnosed with mental illness, danger-uncertainty, appearance, affinity-relationship, and belief-culture are effective factors in attitudes of medical students towards mental illness; their knowledge increase with psychiatry clerkship; however, their attitudes and behaviours do not change to a great extent. Discussion: In light of the research findings, it can be recommended that a program which aims to enable students to achieve metacognitive and behavioral skills; to approach stigmatization in the context of humanism and patient-physician relationship; continues during medical education should be used in stigmatization education.