Oskar Fischer (12 April 1876 – 28 February 1942) was a Czech academic, psychiatrist and neuropathologist whose studies on dementia and Alzheimer's disease were rediscovered in 2008.

[1] Fischer served as a physician-in-chief at the division of neurology and psychiatry of the second garrison hospital in Prague during World War I, and treated many soldiers who had experienced mental difficulties while fighting on the Eastern Front.

After challenging and criticising German medical doctor Halbhuber, his chief at the division, Fischer was transferred to barracks hospital in Pardubice in eastern Bohemia and served there until the end of the war.

[10] In June 1907, based on the reports of Beljahow that had been later affirmed by Redlich and Leri Fischer argued that 'miliary necrosis' should be regarded as a marker of senile dementia.

[11] Then he published an article in 1907, reporting histopathological findings on senile dementia collected from a sample of 16 postmortem brains from elderly subjects.

[16] Pavel Kalvach of the Charles University of Prague pointed out in 2009 that Fischer made arguably even much more important contributions than Alois Alzheimer to the description of the disease.

[16][17] The reasons for neglecting Fischer's contributions included the nationalist tensions and the anti-Semitic approach of his period[16] as well as the academic competition between the Prague and Munich neuropathology schools.