We describe a 45-year-old man who presented with multiple nodules along the tendons of the scapular region, the elbows, wrists, forearms, thighs, and ankles. The patient was a carrier of human T cell lymphotropic virus I (HTLV-I), which was probably transmitted from his mother; his mother also had polyarthritis. Histopathologically, the nodules consisted of numerous, small, fibrinoid masses. The synovium adjacent to the tendon sheath was hyperplastic, with fibrinoid necrosis mimicking rheumatoid synovium. However, synovitis was not present inside the adjacent joint. HTLV-I proviral DNA was detected in the cells of the nodule, in tenosynovial cells, and in peripheral blood lymphocytes, but not in skin fibroblasts. In situ reverse transcription assay showed a high quantity of tax/rex messenger RNA in the proliferating lining cells. Based on these features, we classified this case as an atypical manifestation of HTLV-I-associated arthropathy associated with fibrinoid nodules resulting from chronic tenosynovitis.