April 2020 marks what would have been the hundredth birthday of Professor Thomas Stephen Szasz, who passed away in 2012. This year was also the 60th anniversary of the first publication of his iconoclastic thesis on the “myth of mental illness.” In the present paper, Szasz’s main views on mental illness and modern psychiatry are summarized. By showing the origins of Szasz’s ideas in particular, it describes the following topics: Szasz’s distinction between bodily disease and mental illness, his preoccupation with the progressive medicalization of everyday life, his description of psychiatry as an institution of social control, his critique of the therapeutic state, i.e., the alliance between psychiatry and the state, and his deliberations on liberty, personal freedom and responsibility. While addressing Szasz’s main critics, the paper attempts to show the influence of Szasz’s concept on today’s psychiatry and stresses that despite well-deserved criticism he expressed some of the epistemological and ethical problems of modern psychiatry better than anyone else, which makes his legacy still important for the mental health practitioners of today.