OBJECTIVE Description of a subtype of arthrosis deformans of the hand which is characterised as osteoclastic arthrosis. METHODS Retrospective analysis of radiographs of the hands of 150 women and 100 men with radiological findings of arthrosis deformans. RESULTS 5% of women and 2% of men showed at least one digital joint with subchondral osteolysis of one or both articulating bones involving at least a third of the phalanx. This subchondral osteolysis far exceeds the cysts which are situated in the epiphyseal part of the articular region. It may develop within a year. CONCLUSIONS Osteoclastic arthrosis of the finger is a subtype of polyarthrosis of the hand. Serial observations suggest that an osteoclast stimulating substance is produced by the cysts or arises directly from the synovial fluid; this enters the subchondral part of the bone through clefts which may or may not be visible radiologically and that this produces osteoclastic activity. The most important differential diagnoses are chronic tophaceous gout and a benign tumor.