A 64-year-old Japanese woman with a two-week history of polyarthralgia and persistent cough was diagnosed as seropositive polyarthritis and fulfilled the criteria of early rheumatoid arthritis (RA). In addition, inflammatory pitting edema of the distal extremities was apparent, suggestive of the remitting seronegative symmetrical synovitis with pitting edema (RS3PE) syndrome. A number of investigations including hand MRI, bone scintigraphy and HLA typing supported a diagnosis of RS3PE syndrome rather than RA. Chest computed tomography revealed concomitant evidence of bronchiolitis obliterans organizing pneumonia (BOOP). Treatment with 30 mg of prednisolone daily immediately ameliorated the polyarthritis and the BOOP. Seropositive polyarthritis with distal pitting edema may be categorized as both RA and the RS3PE syndrome.