A surface impedance boundary condition (SIBC) is presented for the finite-difference time-domain (FDTD) simulation of surface-emitting lasers with Bragg stacks. This method eliminates the need to directly implement the actual Bragg stack structure in the FDTD code and enables three-dimensional FDTD modeling of surface emitting lasers such as vertical cavity surface-emitting lasers (VCSELs). The SIBC is derived from the equivalent surface impedance properties at the interface between the cavity and Bragg stack. The three-dimensional finite-difference formula tions of the SIBC are given in this paper. Simulations of VCSELs are performed with both the SIBC and the actual Bragg stack structure. The excellent agreement obtained between these two simulations shows the validity of the SIBC developed in this work.