Fifty-three Japanese patients with the lymphoma-type adult T-cell leukemia (ATL) were analyzed to study the prognostic value of various clinical findings recorded at the time of diagnosis. All patients were positive for human T-cell leukemia virus type I (HTLV-I) antibody and demonstrated monoclonal integration of HTLV-I proviral DNA in their malignant cells. The important individual variables detected in a previous univariate analysis were placed in a multiple regression model to identify the major prognostic factors for survival. This analysis showed that serum lactate dehydrogenase (LDH), calcium, and total protein levels had a strong predictive relationship with the length of survival (in descending order of importance). Among the 53 patients, 46 were dead at the time of analysis. The cause of death in relation to the duration of survival is also reviewed in this article.