Ultrastructural analysis of the surface of the syncytial absorptive epithelium of the aberrant form of human placenta known as hydatidiform mole reveals modifications of the micro-villous apical surface. We have described these features as microgibbosities. They are apparently groups or rings of microvilli greater than the usual length in the surrounding cytoplasm. The existence of such microvilli and the probable consequences for the control of the dynamics of microvillar cytoskeletal elements should be accommodated by future theories of microvillar biogenesis.