The fellow eyes in 84 cases of unilateral idiopathic macular hole were studied retrospectively to determine prognoses and risk factors for this disorder. On initial examination, 15 of 84 eyes (18%) had a macular cystic lesion (group 1), 23 (27%) had a yellow spot in the fovea (group 2), and 46 (55%) had a normal macula (group 3). Of the 84 eyes, 58 (69%) had posterior vitreous attachment. During a mean follow up of 39 months, macular hole developed in 8 of 15 eyes (53%) in group 1, and in 6 of 23 eyes (26%) in group 2. However, a macular hole did not develop in eyes with posterior vitreous separation or a normal macula. Although the risk of developing a macular hole may have been overestimated in our study, posterior vitreous attachment and macular abnormalities may be important in predicting macular hole formation in the fellow eyes in idiopathic macular hole cases.