The flood induced overtopping of dams is one of the most observed failure reasons in history. In this study, the overtopping reliability of Tanyeri Dam is evaluated in a probabilistic manner. To this end, flood hydrographs having two variables and initial water level of the reservoir are randomly generated and the probability of exceedance of the dam crest elevation is evaluated using Monte Carlo simulation. Several scenarios, including the case that both the spillway and the bottom outlet are not working, are considered and their effects on the dam overtopping reliability are assessed. According to the results, Tanyeri Dam is found to be 100% reliable when its spillway operates during a possible flood having 10000-year return period. In addition, it is shown that the maximum reservoir level observed during a flood is directly dependent on the initial water level of the reservoir.