Political prisoners’ suicide in Schlisselburg and other prisons in Tsarist Russia was not uncommon. The opinion that Mikhail Grachevsky attempted to force mitigation of the prison regime and sacrificed himself for the sake of his fellow inmates is generally accepted. While analyzing Grachevsky’s path to the revolution and his personal qualities, the article examines the real reason for his suicide. Soon after his first arrest Grachevsky joined the Narodniks, led propaganda among the workers, for which he was arrested. Three years of solitary confinement, participation in the trial of 193 (1877–1878) formed him as a revolutionary. He was sent into exile to Kholmogory (Arkhangelsk province) and escaped, then joined the revolutionary organization Narodnaya Volya and became a member of its Executive Committee. Numerous arrests of his colleagues in 1881 put him at the forefront of the organization. By the time of his arrest on 5 June 1882 Grachevsky was one of the most experienced revolutionaries, who participated in several terrorist attacks, worked in underground printers and led propaganda in provinces. Not surprisingly, such responsible, dangerous activity had exhausted his nervous system. The future promised only arrest and the gallows, and Grachevsky expected nothing else for himself. He was also tormented by guilt, because he carelessly led the police to the safe apartment where many members of Narodnaya Volya were arrested. He took the most blame and was sentenced to life imprisonment in the trial of 17 (1883). Grachevsky ended up in a prison cell at Schlisselburg, where he committed suicide three years later. The author examines Grachevsky’s medical case as revealed by the official reports of the doctor and jail warden and the memoirs of Schlisselburg’s prisoners and argues that he lost his mind due to harsh imprisonment conditions