Gonarthrosis is most frequently defined as changes involving articular cartilage damage, abnormal bone formation, reactive changes in synovial membrane and pathologic synovial fluid. The site of initial damage remains unknown. It is known presently that in the development of the process, reparative reaction of chondrocytes expressed by increase of synthesis of the main collagen types (type II, in lower degree types IX, VI, XI) and also of proteoglycans, is the primary event, at cell level. The final result of the pathological process in gonarthrosis is imbalance between synthesis of articular cartilage and damage leading to its loss. Each cause or process inducing cartilage degradation exerts effects on the occurrence and progression of gonarthrosis. Gonarthrosis is diagnosed on the basis of clinical and radiological examinations. Magnetic resonance, bone scintigraphy and arthroscopy are also of importance. However, in the future, the markers of articular cartilage destruction products in body fluids would be the key to determination of the time of the onset of the disease, its progression and advances of treatment. Great hopes in the treatment of gonarthrosis could be connected with gene therapy.