As soon as Adolf Hitler came to into power in 1933, four laws on racial segregation and race protection were edicted between 1934 and 1935. Schizophrenia, manic-depressive psychoses, epilepsy and alcoholism were regarded as hereditary mental illnesses. These laws were responsible for the sterilisation of 350,000 individuals who were thought to be at the source of the propagation of hereditary illnesses which might endanger the health and the future of the Aryan Germans. On September 1, 1939, Action T4 was launched: it required that all the mentally ill be exterminated. This action, which was run by the highest level of the Reich's chancellery with the help of psychiatrists coming from all backgrounds including university professors, was supposed to grant a serene death to all the mentally ill considered as untreatable. The death sentences were carried out by the medical staff in psychiatric hospitals specially equipped with gas chambers. Following protests, Action T4 was officially stopped on August 24, 1941, but, in reality, continued until the end of the war. The death sentences were carried out using either lethal doses of medication or food deprivation. One hundred and fifty thousand individuals fell victim to that therapeutic extermination which played an economic role as important as the one deemed to social protection. Many German academics, researchers, psychiatrists, geneticians and anthropologists played and active part in these murders which were carried out in the name of Nazi ideology based upon the supremacy of the Northern Germanic race and the necessity to protect it from miscegenation, especially from Jews. In the final part of this paper, the author gives an explanation of the perversion of ethics carried out by German psychiatrists.