In 1924 Oswald Bumke was appointed as Emil Kraepelins successor to the Chair of Psychiatry at the University of Munich. After 1933 he was a promoting member of the SS and the National Socialist Teachers Federation but he was never a member of the National Socialist German Workers' Party (NSDAP). In 1933 he assumed the presidency of the Society of German Neurologists but only 2 years later he withdrew from the executive board because of scientific and personal differences with Ernst Rüdin, the new "strong man" of the merged Society of German Neurologists and Psychiatrists. After the end of WWII, Bumke affirmed that despite his exposed position as professor of psychiatry during the NS era, he had lacked any influence and that he had sabotaged the "Law for the Prevention of Genetically Diseased Offspring" (GzVeN). He declared that for scientific reasons he had been extremely critical of the GzVeN and even had expressed his views in various publications. Nevertheless, he supported forced sterilization in his treatise "The State and Mental Diseases" published in 1939. His statement that the clinic in Munich had manipulated diagnoses in order to protect patients from eugenic measures and "euthanasia" refers to a potential interference, but as documents are lacking this cannot be substantiated. After 1940 Bumke functioned as a consulting military psychiatrist in expert reports. Political assessments from this period presented him as politically reliable. His biography exemplarily shows that a meticulous juxtaposition of post-war documents with correspondent records stemming from the Nazi period is imperative in order to arrive at a source-critical well-founded and differentiated evaluation.