Purpose: To assess the prevalence and progression of a stage 0 macular hole in the fellow eye of patients with an idiopathic full-thickness macular hole. Methods: The fellow eyes of 189 patients who underwent idiopathic full-thickness macular hole surgery were examined by biomicroscopy and spectral domain-optical coherence tomography (SD-OCT). A subset of 21 fellow eyes with a stage 0 macular hole was observed. Changes in the macular hole were evaluated by biomicroscopy and SD-OCT for an average of 29 months. Results: Among the 21 eyes, 15 showed no change in perifoveal vitreous detachment (71.4%). Two eyes (9.5%) developed complete vitreofoveal separation, and one of the two developed a separation after progression to stage 1A. Among 21 eyes, 5 (23.8%) developed above stage 1A, and one of the five progressed to stage 1B after five years, which was successfully treated with vitrectomy and gas tamponade. Conclusions: Perifoveal vitreous detachment in the fellow eye on SD-OCT, defined as a stage 0 macular hole, occurred at an earlier phase than stage 1A macular holes and may progress to an advanced stage. Therefore, patients who undergo macular hole surgery and have a stage 0 macular hole or perifoveal vitreous detachment in the fellow eye should be followed closely.