Pain and loss of function are the major clinical symptoms leading to the diagnosis of osteoarthritis (OA). Further clinical findings allow the diagnosis of OA with a high level of sensitivity and specificity at the hip, knee and hand. Standard x-rays of the joints confirm the definitive diagnosis while standard serological examinations are mostly only necessary for differential diagnosis. The analysis of synovial fluid is an important diagnostic tool. Many biochemical markers in the serum have been established for anabolic and catabolic substances, which play a role in the synthesis and degradation of bone, cartilage and synovium in OA. These are of high scientific interest, but play only a minor role in daily practise. At present no single clinically important biochemical parameter exists for the early diagnosis, treatment, control or prognosis of OA.