A 17-year-old Cambodian-born female was recently evaluated for subacute seronegative arthritis involving both ankles and the right midfoot. Suboptimal response to a nonsteroidal anti-inflammatory drug prompted open synovial biopsy, which showed intensive eosinophilic infiltration of the synovial structures. Slight peripheral eosinophilia had been found before her admission to hospital, and Ankylostoma duodenale was isolated. Antiparasitic treatment offered little more relief. She was also found out to be a carrier of the histocompatibility antigen HLA B27, and it may be that despite unusual histological findings she had a B27-related reactive type of arthropathy. The relation to the parasitic infestation remains speculative.