To some degree, all optical systems affect the polarization of light passing through them. When this instrumental polarization adversely affects the performance of the system (e.g., the classic Maltese cross artifact in the polarizing microscope), it is said to possess polarization aberrations. Using the polarizing microscope as a model system, we present in this paper an analysis of polarization aberration effects upon 3-D image formation. We have derived analytic expressions for the 3-D point spread function and compared them with experimental observations. We also discuss how one scheme for correcting polarization aberrations performs in 3-D.