We found hyperplasia of the lens epithelium to be the most important feature contributing to opacification of the posterior capsule in a histopathologic study of 77 eyes obtained postmortem after extracapsular cataract extraction. Wrinkling of the posterior capsule appears to be caused by contraction of hyperplastic lens epithelial cells that have acquired myoblastic differentiation. Other cells that rarely grow onto the anterior surface of the posterior capsule include iris melanocytes and pigment epithelium, fibrocytes, and lens epithelium in the form of Elschnig pearls. This report describes the clinical and pathologic features of posterior capsule opacification, outlines the mechanisms of formation and discusses the rational development of strategies designed to prevent and treat this complication.