A 73-year-old man was admitted for insidious cough and exertional dyspnea of 3-year duration. Inspiratory crackles were heard at the lung bases. He was seropositive for human T-cell lymphotropic virus type I (HTLV-I). Chest radiography (Fig. 1) and computed tomography (Fig. 2) showed reticulonodular shadows with honeycomb change in both lungs. Transbronchial biopsy revealed fibrosis of the alveolar septa with infiltration of lymphocytes. Bronchoalveolar lavage fluid contained mononuclear cells with 84.2% T-cells (52.3% CD4 cells, 28.3% CD8 cells) and 2.4% B-cells. The patient was treated with bronchodilators, antimicrobials and oxygen as needed, but died of respiratory failure 4 years later. HTLV-I has been implicated in some cases of interstitial lung disease called lymphocytic alveolitis/pneumonitis. Unlike these cases, our HTLV-I carrier presented with "honeycomb lung." Although the natural history of HTLV-I-associated interstitial lung disease is yet to be known, it may well progress to pulmonary fibrosis with honeycombing over many years. To investigate this possibility, patients presenting with interstitial pneumonia/pulmonary fibrosis should be tested for HTLV-I.