Geotechnical design of earth retaining structures, such as retaining walls, traditionally has been based on a deterministic methodology using fixed Factors of Safety (FS), which does not take into account the intrinsic variability of the soil’s behavior. In order to estimate the uncertainty in the soil’s response, an analysis of the effect of the variability of the geotechnical parameters in the design of retaining walls has been developed, finding that, due the high variability of the geotechnical parameters of the retained and foundation soils, a deterministic analysis may underestimate or overestimate the loads and resistances considered in the process of the retaining wall design. Based on the above consideration, a simplified alternative design approach, based on failure probabilities (instead of a fixed FS), is presented. This approach can lead to better retaining wall designs, which could be less expensive while maintaining the required level of safety and reliability.