A prospective study of 78 eyes with idiopathic preretinal macular gliosis disclosed that 74 of the 78 (95%) had posterior vitreous detachments at the time of the initial examination. A second prospective study of 34 eyes with acute posterior vitreous detachment showed preretinal macular gliosis in three eyes (9%) initially (zero to seven days) and in 14 eyes (41%) after an 18-month follow-up period. These two studies indicated that posterior vitreous detachment may play a role in the development of idiopathic preretinal macular gliosis.