Report on 178 rearthrotomies of the knee joint in 158 patients. Most of these rearthrotomies became necessary subsequent to meniscus operations. A review of the literature shows that these are mainly persisting or recurring complaints appearing usually under the overall pattern of "irritable knee". The principal causes were found to be leftover meniscus residues; on rarer occasions degenerative meniscus regenerates were found, or other causes such as floating cartilage, damaged cartilage of the patella, and instabilities of the condyles and of the ligaments.