From 1974 to 1989 a total of 3447 cases of retinal detachments were treated surgically in three departments of ophthalmology in Hamburg. It was found that 245 (7.2%) of these eyes had previously been subjected to prophylactic coagulation because of lattice degeneration, tears, and retinoschisis. Retinal detachment followed the coagulation in 45% within 1 year in 45% of cases within 10 years in a further 45%, and after 11 years or longer in a further 5%. (In 5% the time of coagulation was unknown). The retinal defects responsible for detachment were within or at the border of the coagulation scars in 66% of cases. In this group the time interval between the coagulation and the occurrence of retinal detachment was half that in the eyes in which defects developed in the untreated retina. The obvious faults of the prophylactic coagulation are discussed.