The article outlines the euthanasia murder of Jewish patients of mental hospitals in the former German “Reich” according to our present knowledge. It focuses on the special operation organized from Berlin in 1940 / 1941 as part of the Nazi euthanasia and gassing operation (“Operation T4”). The article is based on regional studies published since Henry Friedlander’s pioneering work, “The Origins of Nazi Genocide: From Euthanasia to the Final Solution” of 1995. The first attempt to collect proof of the deaths of Jewish patients was undertaken by Heinz Faulstich in 2000 and will be continued. The result is that we now know the names of 1,740 Jewish victims as compared to the former 1,026. Finally, attention will be drawn to the lack of detailed description in the planning of “T4” carried out centrally in Berlin, and of its gradual realization in the different parts of the German “Reich”.