The area of scientific focus of academician L.A. Ilyin — radiation medicine and radiation protection. According to his ideas and with his direct participation, medical-biological facilities and special systems of protection against one of the nuclear weapons types have been developed. Veteran of special risk units, from the first days after the accident at the Chernobyl nuclear power plant he was in the center of damage, was one of the scientific leaders that headed medical-biological and hygienic work aimed at mitigating the disaster consequences, was taking responsible decisions on the strategy and tactics of protecting the liquidators and the population. Leonid Andreevich Ilyin is the first scientist in the world who developed and substantiated the forecast of radiological consequences of this catastrophe, later confirmed by leading foreign and domestic experts. And furthermore Leonid Andreyevich is a man with an incredibly young, perky smile, lively eyes and memory that stores many amazing details which have already become history today. What lessons we need to draw, why nuclear powers are particularly accountable to humanity and what are the secrets of active longevity — our conversation dwells on all this.