Three cases are described of acute glaucoma following vitrectomy and silicone oil injection in proliferative vitreous retinopathy. The first case developed silicone-induced pupillary block in a phakic eye. Cases 2 and 3 developed elevated pressure in aphakic eyes with deep anterior chambers. Cases 1 and 3 were treated by laser iridectomy. Case 2 was treated by removal of silicone. The pathogenesis and treatment of these problems are discussed.