[en] This report presents the results of the second phase of the National Radon Survey carried out by the Radiological Protection Institute of Ireland. The counties included in this phase are Carlow, Donegal, Kildare, Kilkenny, Laois, Leitrim, Longford, Meath, Offaly, Roscommon, Sligo, Waterford, Westmeath and Wexford. The average radon concentrations for the houses measured in these counties ranged from 63 to 147 Bq/m³ wth individual values as high as 1562 Bq/m³. The measurement data were grouped on the basis of the 10 km grid squares of the irish National Grid System and used to predict the percentage of dwellings in each grid square which exceeds the Reference Level of 200 Bq/m³. Grid squares where this percentage is predicted to be 10% or higher are designated High Radon Areas. The health effects of exposure to high radon levels are discussed and recommendations are made regarding both new and existing dwellings. (author)