A variety of pathological changes of the vitreous endanger the function of the retina and are therefore reason for removement of the vitreous body. The most important technique is the pars plana vitrectomy, which allows to perform the surgical manoeuvre on the stabilized eye. Different indications for vitreoretinal surgery are discussed, as well as materials, which are used for replacement of the vitreous. When long standing replacement of the vitreous is necessary in complicated cases, silicon oil is the most important material.