Three cases of osteoarthritis due to dematiaceous fungi are reported. The first case, a Drechslera longirostrata spondylitis complicating prosthetic valve fungal endocarditis responded only to the association of Amphotericin B and Ketoconazole. The second patient had chronic osteoarthritis of the knee due to Phialophora parasitica resistant to medical and surgical treatment after renal transplantation. These two cases are the first and the second known reports of clinical infection with these fungi. The third patient had osteoarthritis of the patella complicating a skin infection by a thorn prick. This was cured by surgical excision and 3 months' medical treatment. These cases of infections osteoarthritis of the knee followed subcutaneous abscesses. Deep tissue infections with dematiaceous fungi with osteoarthritic involvement are very rare (6 cases of Drechslera and 8 cases of Phialophora have been reported). These fungi are opportunist saprophytes of plants in subtropical regions. They are characterised on culture by their brown and black pigmentation and microscopy shows septated filaments. Cutaneous effraction is the usual portal of entry in man; patients commonly have depression of their immune systems. Osteoarthritis is generally due to local extension of a subcutaneous abscess. The functional sequellae can be very serious. Treatment comprises surgical excision of the infected tissues with antifungal drugs which may have to be given in association.