Lymph nodes in incipient adult T-cell leukemia-lymphoma with Hodgkin's disease-like histologic features. Lymph nodes were examined from four patients with incipient adult T-cell leukemia-lymphoma (ATLL) who had mild lymphadenopathy, fatigue, no or a few atypical lymphocytes in their peripheral blood, and integrated proviral human T-cell lymphotrophic virus type I (HTLV-I) DNA in the nodes. The HTLV-I DNA was detected by southern blot analysis and/or polymerase chain reaction in the lymph nodes of all cases. The nodal architecture was preserved. Some scattered or aggregated highly lobular, cerebriform, or Reed-Sternberg-like giant cells were observed, with occasional mitoses and diffuse infiltration of small to medium-sized lymphocytes, with no or minimal nuclear abnormalities in the enlarged paracortex. The giant cells were usually positive for Ki-1 and also for UCHL-1 and other T-cell markers but negative for Ber-H2. Rearrangement and/or deletion of T-cell receptors were found in three of four patients. All patients died within 2 years, with transformation to overt leukemia-lymphoma occurring in three patients, and pulmonary carcinoma in one. The incipient or prelymphomatous phase of ATLL should be differentiated from Hodgkin's disease because of the distinctly different prognoses of these two diseases. 