In Switzerland the regions with the highest wind energy potential are the Jura range, the Alps and the Alpine foothills. During the winter months, the air temperature in these regions is frequently below freezing for lengthy periods of time. This results in the formation of ice on measurement instruments and rotor blades. The calculations of icing frequency are based on comprehensive data pertaining to cloud moisture, temperature and wind speed obtained from an analysis of the SwissMeteo COSMO-2 weather forecasting model. The icing model calculates the ice load on a cylindrical, freely rotating structure. The icing frequency covers a 2.2-kilometre grid and has been verified on the basis of measurements carried out in the Alps at IMIS (Integrated Measurement and Information System) stations and by other measurements carried out in the Jura region. The indicated frequencies are modelled figures. They provide an indication of where icing can occur in Switzerland. Measurements directly on site are essential in order to record the development at a given location.