Geological models are often used in assessments of groundwater resources and groundwater vulnerability, and often in connection with numerical groundwater models. As the uncertainties of the geological models will most likely affect the results of the subsequent calculations and assessments, it is important to describe the uncertainties related to the geological model. A comprehensive assessment of the uncertainties of the geological model is, however, a complicated task. The nature of the data sets included in the geological model is normally very heterogeneous and every data set has uncertainties of its own. In addition to this, the geological interpretations performed during the geological modelling have a high degree of subjectivity. As quantification of the uncertainties of the geological model as a whole is complicated, a simple method for qualitative assessment of the uncertainty of the geological model is proposed. The method takes the uncertainties related to the data sets, the density of data points, as well as the uncertainties related to the geological interpretations into consideration.