The use of segmented mirrors for the primary elements of large telescope systems is becoming increasingly popular owing to the cost effectiveness of the design. Likewise, the use of nonoptically flat glass in large collectors can further reduce cost. Unfortunately, both nonoptical flatness and segment misalignment result in phase errors. If the segmented mirror is not imaged at the detector plane, errors in the measured polarization state may result. We have developed a computer simulation of an optical system, using angular propagation to propagate a two-component-wave electric field from element to element. We use this simulation to study the effects of mirror surface errors on the polarization state of an optical beam. We report herein on the effects of surface warping and of segment piston and tilt on the Stokes parameters of an optical beam reflected from a segmented mirror. When Stokes parameters are averaged across the detector plane, we find no significant error in these averages due to mirror surface errors. However, Stokes parameters at points in the detector plane can have significant errors if there are significant variations in the Stokes parameters of the incident field and there are significant errors on the mirror surface.