The present study aimed to determine the long-term safety and efficacy of chimeric anti-CD 20 antibody rituxan (rituximab, Biogen IDEC, San Diego, CA, USA; Genentech, South San Francisco, CA, USA) in combination with cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) chemotherapy in previously untreated patients with aggressive non-Hodgkin's lymphoma (NHL). Thirty-three patients with previously untreated aggressive B-cell NHL received six infusions of rituximab (375 mg/m(2) per dose) on day 1 of each cycle of CHOP chemotherapy, given on day 3 of each cycle of therapy. Currently, the patients now have a median follow-up of 63 months (range 34 - 82 months). The overall response (OR) rate was 94% and the complete response (CR) rate was 61% at the end of therapy. Of the 33 patients, 2 patients experienced disease progression and subsequently died of their disease, 2 patients experienced disease progression but were alive at last follow-up following additional therapy, and 2 patients died without experiencing disease progression: one due to a cerebral vascular accident at 9 months after therapy and a second patient due to small cell lung carcinoma at 55 months. The 5-year survival rate was 88% (95% confidence interval (CI) 72 - 97) and the 5-year progression-free survival was 82% (95% CI 64 - 93). There were no long-term adverse events noted directly related to the rituximab. The long-term follow-up of patients in this phase II trial of rituximab with CHOP chemotherapy for previously untreated aggressive NHL demonstrates a high response rate, which remains very durable with high 5-year overall and progression-free survivals.