One hundred thirty eyes of 126 patients with idiopathic macular holes were studied by means of indirect ophthalmoscopy, biomicroscopy, color fundus photography, and fluorescein angiography. Posterior vitreous detachment was absent in 61% of these eyes; opacities interpreted as opercula were found in 78 eyes (60%). Forty-nine fellow eyes were followed up for a mean period of 47 months. Eight of 28 fellow eyes without posterior vitreous detachment and none of 21 fellow eyes with posterior vitreous detachment developed macular holes, suggesting that vitreous attachment to the macula is closely related to the development of macular holes. The difference between the incidences of macular hole development in eyes with and without posterior vitreous detachment is statistically significant.