RADIOACTIVE fallout from the Chernobyl accident reached Ireland in May 1986 and caused serious concern with regard to its possible effects on health. Reports of a large scale American study claim an almost immediate effect of Chernobyl fallout in terms of increased mortality rates. A study of Irish mortality rates reported a substantial increase in numbers of deaths during the three months immediately post-Chernobyl. The present study investigates whether there is a statistically significant basis for the reported increase in mortality in Ireland. No discernible evidence was found for increased motality rates in Ireland during 1986, following the Chernobyl accident. The initial report of increased mortality rates was based on provisional mortality registration statistics and not on actual day by day data. © 1989 Springer.