Not many civil engineering technical documents confront an uncertainty comparable to the existing one in the calculations of the geotechnical risk in the Peruvian Andes. The reason of this uncertainty is the dispersion of values of calculation variables that engineers have to input into their models. After many research studies, it has been possible to obtain "reliability curves" about Andean slopes at the Peruvian North region. These curves represent the risk and reliability level for static and pseudo-static conditions (severe seismic conditions), having been determined that a reliability index greater than 2 is acceptable considering the uncertainty of soil and rock geotechnical parameters in the studied region. Analyses are made in order to establish a correlation between the estimated factor of safety, the reliability index, the terrain slope, and the corresponding vulnerability levels. It was found that in order to achieve an acceptable reliability level, the slopes should be less than 36 degrees with a static factor of safety of at least 1.25. Finally, for several history cases presented on professional practice and with the results of this research, it was possible to choose the best alternative of engineering solution, which will be directly associated to a certain cost of losses that would occur in the case that no solution will be adopted for the slopes on study. © 2011 ASCE.