On April 26, 1986, Dyatlov supervised a test at Reactor 4 of the nuclear plant, which resulted in the worst nuclear plant accident in history. In 1987, he was found guilty "for criminal mismanagement of potentially explosive enterprises" and was sentenced to ten years in prison. He was released in five years. He wrote a book in which he claimed that poor plant design, rather than plant personnel, was primarily responsible for the accident.
During the accident, Dyatlov received a radiation dose of 390 rem (5.5 Sv). He died of heart failure in 1995.