OBJECTIVES: To determine the rate of anatomical closure of idiopathic macular holes undergoing vitreous surgery with respect to preoperative horizontal diameter as determined by optical coherence tomography (OCT) and to correlate postoperative visual acuity, duration of symptoms, and late reopening with initial idiopathic macular hole diameter by OCT. MATERIALS AND METHODS: Forty eyes of 40 patients with an idiopathic macular hole were examined with OCT before and after vitreous surgery. All eyes were treated with pars plana vitrectomy, peeling of posterior cortical vitreous, and dilute perfluoropropane or sulfur hexafluoride gas. Face-down positioning was maintained for 7 to 14 days. RESULTS: Twenty-two (92%) of 24 eyes with a preoperative idiopathic macular hole diameter smaller than 400 microm measured by OCT attained anatomical closure following surgery. Anatomical closure was observed in 9 (56%) of 16 eyes with a macular hole diameter of 400 microm or larger measured by OCT (P =.02). The median postoperative visual acuity improvement was 4 Snellen lines in the 31 eyes achieving anatomical closure and no change in the 9 eyes not achieving anatomical closure (P< .001). Late macular hole reopening at longer than 6 months occurred in 3 (10%) of 31 eyes with an initially closed macular hole. This event was observed only in macular holes 400 microm or larger measured by OCT. The preoperative macular hole diameter (P =.02) and duration of symptoms (P =.02) were factors predictive of anatomical closure of the macular hole postoperatively. CONCLUSIONS: The postoperative closure of idiopathic macular holes following vitreous surgery was related to the preoperative macular hole diameter determined by OCT, with lesions smaller than 400 microm demonstrating higher success rates. A trend toward greater visual acuity improvement was demonstrated for idiopathic macular holes smaller than 400 microm. Late reopening was only seen in macular holes that were 400 microm or larger measured by OCT. Preoperative analysis and measurement of idiopathic macular holes with OCT may help delineate postoperative expectations for successful anatomical closure of the macular hole, visual acuity, and long-term closure.