Sergei Sergeyevich Korsakov (Russian: Серге́й Серге́евич Ко́рсаков; 22 January 1854, Gus-Khrustalny – 1 May 1900, Moscow) was a neuropsychiatrist from the Russian Empire, known for his studies on alcoholic psychosis. His name is lent to the eponymous Korsakov's syndrome and Wernicke–Korsakoff syndrome.