A procedure is presented for the analysis of the stability and propagation of cracks in arch dams based on linear elastic fracture mechanics and three-dimensional boundary element modeling. A simplified crack propagation criterion is employed and the crack trajectories arc obtained by multistep extension. The first up stream cracking which occurred in the Kolnbrein arch dam is studied in detail under various conditions conceming the foundation interface, location of crack initiation, reservoir water level and load combinations. Crack trajectories close to the observed one are obtained with water level at 1, 850-1, 860m, which agrees with the prototype experience. It is found that the hydrostatic load and associated uplift pressure on the crack surfaces are the key factors for causing an initial crack at the dam base to propagate to the upstream face. It is also noted that the bonded condition at the interface between the dam and the upstream elevated foundation is responsible for producing the distinctive profile of the observed crack, which daylights on the upstream face at an acute angle.