For the past two decades, archaeologists have been constructing predictive archaeological models to determine the occurrence probability of archaeological sites. Here, the technique has been used to explore the environmental factors that may have had an influence on the distribution of ringforts in Ireland. In the Inny River catchment of the Irish midlands, locational information, together with corresponding environmental variables, were assembled in a geographic information system. The analysis showed that ringfort sites have a distinctive locational pattern and cluster on moderately fertile, well-drained soils on gently sloping land surfaces (slopes of 4–9%) between 80 and 150 m above mean sea level. To test the practical applicability of the model, the results were extended to two separate areas adjoining the Inny River catchment (Blackwater valley and Lough Ramor catchment) in the form of a probability surface. The model predicts relatively low densities of ringforts in the Blackwater valley and much higher probabilities of occurrence in the Lough Ramor catchment. These predictions are broadly consistent with recorded site distributions. © 2006 Wiley Periodicals, Inc.