​The transition from theoretical results to real results is often the critical step in the decisionmaking process of a geotechnical engineer. The proposed method for the reliability analysis of slopes calculates the theoretical solution and then modifies it to account for qualitative information. The first step involves calculation of the probability of failure on the basis of available information from the idealized geotechnical structure. This theoretical probability is then modified by a quality factor to yield an accrual probability of failure. Qualitative aspects are represented by verbal statements that are translated to belief/importance factors in the form of membership functions; the processing of this information is based on fuzzy logic. The results of corrected probabilities of failure are compared with experience-based predictions made by Lambe in his Terzaghi Oration at the Eleventh Conference of the International Society for Soil Mechanics and Foundation Engineering. Data from sociological studies and questionnaire-based measurements of risk acceptance are presented. The corrected probability of failure is then compared with the membership function of the acceptable risk to establish a measure of the urgency of repairs. The approach is implemented in a computerized decision support system incorporating extensive support information and recommendations.