A consecutive series of 55 eyes of 50 patients who received silicone tube implant surgery is reviewed. Seven patients had neovascular glaucoma and 43 had refractory nonneovascular glaucoma, for which previous surgery was unsuccessful. A minimum follow-up of one year (mean, 18 months) was achieved for 30 eyes of 30 patients. For these eyes, the success rate (as defined by an intraocular pressure of 25 mm Hg or less, with or without medication) was 80%. Visual acuity was maintained or improved in 67% of eyes. The complications encountered in the overall study of 55 eyes are discussed, and six main causes of failure are identified. These include exposure of the silicone tube from erosion of the overlying conjunctiva; blockage of the proximal orifice of the tube; corneal decompensation secondary to tube touch; extrascleral tube compression proximal to the gutter; blockage of the distal orifice of the tube beneath the gutter; and insufficient aqueous absorption from the encapsulated area surrounding the 360 degrees encircling gutter. Revision surgery was required in 21 eyes (38%). Two alternative methods for insertion of the silicone tube (a "cyclodialysis approach" and a "trabeculectomy approach") are described, and their complications are compared. The incidences of tube exposure, choroidal detachment, and flat anterior chambers were far higher in the trabeculectomy group. The cyclodialysis group had an increased incidence of hyphema and corneal endothelial touch by the tube.