Purpose: To describe new details of epiretinal cell proliferation in flat-mounted internal limiting membrane specimens. Methods: One hundred nineteen internal limiting membrane specimens were removed en bloc with epiretinal membranes from 79 eyes with macular pucker (MP) and 40 eyes with vitreomacular traction syndrome. Intraoperatively, posterior vitreous detachment was assessed as complete or incomplete. Whole specimens were flat-mounted on glass slides and processed for interference and phase-contrast microscopy, cell viability assay, and immunocytochemistry. Results: Mean cell viability percentage was higher in MP than in vitreomacular traction syndrome. Two cell distribution patterns were found. Anti-CD163 labeling presented predominantly in MP with complete posterior vitreous detachment. CD45 expression was similar in all groups of diagnosis. Anti-glial fibrillary acidic protein (GFAP) labeling was found in MP irrespective of the extent of posterior vitreous detachment. Alpha-SMA (alpha-smooth muscle actin) labeling was mainly presented in MP with incomplete posterior vitreous detachment and in vitreomacular traction syndrome. Simultaneous antibody labeling included GFAP/CD45, GFAP/CD163, CD163/CD45, and CD163/alpha-SMA. Conclusion: Hyalocytes constitute a major cell type of epiretinal cell proliferation in eyes with MP and vitreomacular traction syndrome. Glial cells, notably retinal Muller cells, are involved as well. It appears that transdifferentiation of cells in vitreomacular traction might be more frequent than previously thought and that those cells possess a greater variability of immunocytochemical properties than expected. RETINA 33:77-88, 2013