This paper deals with probabilistic slope stability analyses of earth-fill dams. Hydraulic conductivity, unit weight, cohesion and internal friction angle of the soil are considered as random variables. Seepage flow through the dam body is solved by Monte Carlo simulation method (MCSM). Reliability analyses of both upstream and downstream slopes of the dam are performed with reference to variations in pore water pressure using MCSM. Five different limit equilibrium methods are utilized for slope stability calculations. Soil sampling frequency is shown to be an important issue in the analyses. Also, the effect of stochastic seepage flow model on slope stability analysis is investigated. Deterministic seepage flow model is proved to cause underestimated reliability indices in probabilistic slope stability analysis.