Adult T-cell leukemia/lymphoma (ATL) is a neoplastic disorder of T lymphocytes associated with human T lymphotropic virus type I (HTLV-I). The prognosis of ATL is generally poor. We present here a 79-year-old woman with spontaneous remission of acute type ATL. Spontaneous remission was preceded by surgical biopsy and pneumonia and lasted for two years until she died with pancreas cancer. Monoclonal integration of HTLV-I provirus DNA became undetectable after remission.