Subtotal open-sky vitrectomy can be used to improve visual function in some eyes for which closed vitrectomy is useless. Open-sky vitrectomy allows easier access for surgical instruments, especially to anterior fundus structures. The technique also improves the visibility of intraocular structures. The surgical procedure, which uses special instruments and high-molecular-weight hyaluronic acid, is divided into four stages: preparation, operating inside the vitreous cavity, wound closure, and retinal reattachment. In 290 consecutive operations for which complete follow-up data are available, retinal reattachment was achieved in 61 eyes (21%). The greatest number of successes (16 of 30 cases [53%]) was achieved in severe tractional retinal detachments. Such results are encouraging because these eyes were considered inoperable by other techniques. Open-sky vitreous surgery is performed through a corneal incision, but a scleral incision over the pars plana may become the method of choice in selected cases. The development of a preretinal fibrin membrane, as a result of either a closed vitrectomy or an open-sky procedure, may be a major cause of postoperative failure. Hypotony during surgery is probably the main precipitating factor of intraocular fibrin membrane formation.