The monitoring of an earthfill dam during the various phases of the construction and service is a crucial process to investigate the performance of the dam from the safety point of view. Monitoring is carried out through installing the instruments at the critical locations. In the present paper, instrumentation data and the numerical analyses have been used for the monitoring of Mahabad earthfill dam, Iran. Numerical analyses were carried out using Plaxis and Sigma-W. Considering the good agreement between the measured data and the values predicted by Plaxis and Sigma-W, it can be concluded that the numerical models developed in the present paper are accurate enough to be used for the analysis of earthfill dams.