Massive periretinal proliferation (MPP), a serious complication of retinal surgery is caused by proliferation and fibrous metaplasia of cells mostly deriving from retinal pigment epithelium and retinal glial cells. Contracting fibrous membranes in the vitreous and on and also under the retina cause the intraocular changes of MPP. Early signs such as increased "tobacco dust," pigmented clumps in the vitreous, subtle preretinal and even retroretinal membranes are usually overlooked. The late signs such as starfolds, irregular retinal folds and funnel-shaped detachments are well known. The pathogenesis of the clinically visible signs is described and a four stage classification of the disease is given. Based on the improved understanding of this disease, a new therapeutic approach is presented, with the technique of pars plana vitreous surgery. Not only vitreous membranes but also preretinal membranes are removed. Forty-seven consecutive patients who suffered from severe massive periretinal proliferation were operated on with this technique and followed for six months or more. Seventeen patients (36%) had an attached retina. Twelve patients had a major visual improvement. The major postoperative complication is phthisis bulbi (10 eyes, 21%).