This paper reports the results of a medical research that measured prejudice and attitudes towards mentally ill people and towards the mental illness. Three groups of respondents were studied: medical students, psychology students and the general population. Medical students and psychology students represented a population that is educated in regards to mental illness, and the general population was not trained so much about mental illness. The hypothesis was that the respondents who have been working with mentally ill people and had lots of knowledge about mental illnesses were the persons with less prejudice towards people with mental illness. The main objective of research was to examine the differences in prejudice and attitudes between respondents who had experience and knowledge related to mental illness and people with mental illness compared to those without such knowledge and experience. Testing was conducted using an anonymous online survey consisting of thirteen questions. The research confirmed the hypothesis and it could be an incentive for education aimed at specific groups.