Few cases of diffuse panbronchiolitis (DPB)-type HTLV-1-associated bronchiolo-alveolar disorder (HABA) have been reported for its long-term outcome. Here we present a case of a 55-year-old man with HABA, followed up over 9 years. He developed chronic bronchitis at 45 years old, and suffered from recurrent respiratory infections thereafter. At the age of 55, he was referred to our hospital due to DPB refractory to macrolide treatment. His HTLV-1 antibody test was positive and 31% of white blood cells were adult T-cell leukemia (ATL) cells. Transbronchial lung biopsy showed no infiltration of ATL cells. Based on these findings, a diagnosis of DPB-type HABA with chronic ATL was made. He had no poor prognostic factors. After 8 years' careful follow-up, he showed acute conversion from chronic ATL and despite aggressive treatment, he died of sepsis at 63 years old. During the follow-up, centrilobular nodules on chest computed tomography were attenuated but bronchiectasis developed gradually, although he rarely experienced episodes of severe lower respiratory infection. Concurrently, severe airflow limitation with air trapping developed and non-invasive positive pressure ventilation was introduced 1 year before his death.