Accident of Chernobyl nuclear power plant. From rumors to the reports of international organizations. WHO, IAEA and others summary reports of one and two decades after and UNSCEAR 2008 of 25 years after Chernobyl accident

False rumor was circulating at a disaster, Nuclear disaster was not an exception. The author could visit the spot in 1990 after Chernobyl accident when the old USSR started international exchange, take part in various research projects with countless visits till ten years after and attend international organization's summary report conference of one and two decades after. Scientific investigation on radiation hazards became possible and results of various investigations had been reported. Evaluation of scientific credibility of reports came to a big job, which required the author's great effort to give an international scientific consent such that thyroid cancer in childhood was caused by the consequences of the accident with chronological and geographical strong circumstantial evidence. This article reviewed chronological definite information and experiences of radiation hazards that the author got from initial false rumor age to the publication of summary reports of international organizations, and presented problems for emergency response at nuclear disaster. (T. Tanaka)