The outcome of patients with transformed diffuse large-cell lymphoma is poor. High-dose chemotherapy and autologous peripheral blood progenitor cell (PBPC) transplantation is the treatment of choice for patients with relapsed nontransformed diffuse large-cell lymphoma. The role of transplantation for transformed lymphoma is poorly studied. We retrospectively reviewed 118 consecutive diffuse large-cell lymphoma patients undergoing autologous PBPC transplantation from 1994 through 1999 and compared 18 transformed diffuse large-cell lymphoma patients with 100 nontransformed patients. The transformed patients were more likely to be older (median age, 52 years vs. 45 years, P = 0.03), had a longer time from diagnosis to transplant (median, 35 months vs. 10 months; P < 0.0001), were more likely to have bone marrow involvement at diagnosis (61% vs. 15%, P = 0.0001), and were more likely to have had 2 or more courses of prior chemotherapy (94% vs. 71%, P = 0.04) than were nontransformed patients. Ninety-nine percent of patients received high-dose busulfan/cyclophosphamide/etoposide as the transplant preparative regimen. Event-free survival and overall survival were similar in the two treatment groups. Four-year overall survival was 53% in the nontransformed group versus 61% in the transformed group; 4-year event-free survival was 37% in the nontransformed group versus 38% in the transformed group. We concluded that autologous PBPC transplantation is a viable and potentially effective treatment option for patients who have transformed diffuse large-cell lymphoma.