Developing an intraocular drug delivery system (DDS) is urgently needed because most vitreoretinal diseases are refractory to conventional pharmacological approaches; eye drops and systemically administered drugs cannot deliver therapeutic drug concentrations into vitreoretinal tissue. Intraocular DDSs address this problem. Intraocular sustained-drug release via implantable devices or injectable microparticles has been investigated to treat vitreoretinal diseases. A nonbiodegradable implant was first used in 1996 for cytomegalovirus retinitis secondary to the acquired immunodeficiency syndrome. Biodegradable implants, composed of hydrophilic or hydrophobic polymers, in the shape of rods, plugs, discs or sheets have been investigated. An injectable rod is presently being assessed in a Phase III trial to treat macular oedema secondary to diabetic retinopathy or branch-retinal vein occlusion. Intraocular DDSs using a biodegradable implant may soon be successfully used to treat serious intraocular disorders.