A numerical model called MIKE21 was evaluated for simulation of dam and dike breaks. In recent years inIran and other parts of the world some dike-breaches have been reported. Application of two-dimensional models in simulation of dike-breaches is inevitable, because of the nature of the flood propagation after the break. However, inIran, there are very few two-dimensional models used in river and floodplain issues. Hence, the performance of MIKE21 as a numerical model for simulation of dike break was investigated in this research. MIKE21 was originally developed for flow simulation in coastal areas, estuaries and seas. MIKE21’s performance in simulation of dam and dike-break was studied via comparison with analytical solutions, other numerical approaches and available experimental data. Fair agreement has been observed, but care should be taken when modeling shock waves with MIKE21. The study was finally extended to a real case study. Some dike-break scenarios were considered in theHellehRiver, inIranand the results are discussed and presented.