The Mantaro Hydroelectric Project generates almost half the electricity of Peru, therefore the safety of the dam is of vital importance to the country. The slopes along the Mantaro River are prone to large landslides, such as the Mayunmarca landslide, located about 1 km downstream of the project's dam, which is the largest landslide recorded in the Western Hemisphere. As part of a comprehensive evaluation of the project stability conditions and risks, three dimensional visualization and analysis techniques have been implemented to model and visualize the complex geologic environment and stability conditions of the reservoir slopes. These tools have improved the understanding of the behaviour of the slopes in a way that was not possible using conventional two dimensional representations and analyses. This paper describes the methodologies and tools used to successfully implement three dimensional techniques for the evaluation of a ten million cubic meter landslide in the Mantaro Hydroelectric Project.