This report describes a patient who developed human T-cell leukemia virus type I-associated myelopathy (HAM) following a living-donor liver transplantation (LDLT) for liver cirrhosis due to hepatitis C virus (HCV) infection. Both the recipient and the living donor (his sister) were human T-cell leukemia virus type I (HTLV-I) carriers. Since the LDLT, he had been treated with immunosuppressive drugs such as tacrolimus and steroids as well as interferon-alpha to prevent rejection and a recurrence of the HCV infection, respectively. Even though the HTLV-I proviral load had decreased upon interferon treatment, he developed a slowly progressive gait disturbance with urinary disturbance 2 years after the LDLT and was diagnosed with HAM. This appears to be the first report of HAM development in an HLTV-I-infected LDLT recipient.