The morphology of the vitreoretinal border region and possible age-related changes in its thickness and its structural elements have been investigated by scanning and transmission electron microscopy. The material comprised both eyes from one human fetus and 15 adults. The age distribution of the adults was two persons in each decade from the third to the tenth decade. Four regions in each eye were studied. The inner limiting membrane (MLI) of the fetal eyes was very thin, of almost equal thickness in the four regions, being thickest in the macular region. The MLI followed the contour of the MÜller cells. A regional difference in thickness of the MLI was found in all adult eyes; it was thickest in the macular region. The outer cellular surface of the MLI was undulating, whereas the inner vitreous surface was smooth. No significant correlation between age and thickness of the membrane could be demonstrated in adult eyes. The diameter of the previously described fibrils close to the MLI varied slightly from approximately 15 to 30 nm. No correlation between age and fibril diameter or fibril diameter and region was found. Fibril length varied significantly between the four regions, the longest being in the ora serrata region, the second longest in the equatorial region, the next in the optic disc region and the shortest in the macular region.