Leukemia is a well described cause of arthritis. Articular manifestations may be present for months before the diagnosis of leukemia becomes evident. Leukemic arthritis may mimic other diseases. The etiology of leukemic arthritis can be diverse, but is often attributed to leukemic involvement of synovium. We describe a case where evaluation, including immunofluorescent and electron microscopy of open synovial biopsy specimens, revealed no obvious cause of the arthritis.