The clinical entity of posterior vitreoschisis, splitting of the posterior cortical vitreous, is not well known. We confirmed its presence biomicroscopically in cases with posterior vitreous detachment and found it mostly associated with retinal vascular diseases, usually manifesting as two dense vitreous membranes with defects. When posterior vitreoschisis develops in an otherwise normal eye, it may not manifest as two membranes, but can form a crescent-shaped, optically empty space in the posterior vitreous cavity. Because its management is different, posterior vitreoschisis should be differentiated from other, apparently similar, conditions, especially posterior vitreous detachment.