1. The magnitudes of the statistical variability of physical and mechanical characteristics of soils and loads have a decisive effect on the probability scatter of stresses, strain and safety factors as well as on the level of reliability of a dam. 2. The given method of estimating reliability makes it possible to determine the probability that a dam will not reach the limit state of the first group (B) and expected value of the safety factor (¯Ks). The use of these criteria in calculating structures opens the possibility of a well-founded determination of the level of reliability of earth dams in coordination with the calculated coefficients of the method of limit states. 3. The level of reliability of an earth-rock dam with a height of 350 m with respect to the most dangerous surface of sliding (with the soil characteristics used in the calculation on the basis of analogues) is 0.999941, which is higher than the level of reliability corresponding to a first-class structure. This provices safe operation of a real dam with a sufficiently economical profile in the case of a possible increase of the variability of soil characteristics during construction.