The Alps are one of the regions where the highest UV levels are measured in Europe. Solar UV radiation increases with altitude mainly due to decreasing amounts of air molecules, ozone, aerosols, and clouds in the atmosphere as well as due to snow covered surfaces. The altitude effect plays an important role in the understanding of the UV radiation field in mountainous terrain. Therefore simultaneous measurements of erythemal UV radiation (broadband) on three different heights were performed in the Alps over more than four years. Under clear-sky conditions, the altitude effect of daily noon-time yearly mean values of direct, diffuse, and global erythemal UV radiation results in 17.4%/1000 m (direct), 8.5%/1000 m (diffuse), and 10.7%/1000 m (global). Seasonal variations of the altitude effect are mainly influenced by changes of solar elevation, albedo values, and turbidity levels during the year. Measured altitude effects are also compared to calculated values obtained by the MODTRAN radiative transmission model.