Treatment with cyclophosphamide, doxorubicin, vincristine and prednisolone (CHOP) has been considered as the standard therapy for diffuse large B-cell lymphoma (DLBCL) for more than 20 years. CHOP treatment in combination with targeted immunotherapy, rituximab (R-CHOP), resulted in significant improvements in the treatment of this group of patients. In this study, efficacy of R-CHOP and R-CHOP-like treatments was analysed. Results were compared to the data of historical patients only receiving CHOP treatment or CHOP-like treatment. Between September 2002 and April 2005, 140 newly diagnosed, untreated DLBCL patients started to receive R-CHOP treatment in a single centre. The eligibility criteria included advanced stage (clinical stages III-IV), or large tumour size (>7 cm) and/or symptom B or extranodal manifestation in the case of clinical stages I-II. The results were compared to the data of 130 patients only receiving CHOP treatment in the past. In the patients receiving R-CHOP, the therapeutic outcomes were superior for all parameters. During an average follow-up period of 44 or 52 months, the overall remission rate was 73.6% in the R-CHOP group in comparison with 47.7% in the CHOP group. The 5-year overall survival was 68.6% vs. 41.0% (RR: 0.4293, CI: 0.2963-0.6221; p < 0.0001), the event-free survival was 59.8% vs. 33.5% (RR: 0.5038, CI: 0.3606-0.7038; p < 0.0001) and the progression-free survival was 64.4% vs. 37.6% (RR: 0.4915, CI: 0.3442-0.7019; p < 0.0001). Since prognostic parameters were more favourable in the R-CHOP group, patient groups were also compared using the International Prognostic Index score. Again, significant differences were revealed by the subgroup analyses. The 5-year overall survival was 74.4% vs. 47.9% (RR: 0.4475, CI: 0.2418-0.8285; p = 0.0084) and 52.0% vs. 28.8% (RR: 0.4989, CI: 0.3098-0.8035; p = 0.003) in the group with good prognosis and in the group with poor prognosis, respectively. In the group with very good prognosis, the statistical difference between the two groups in terms of the 5-year survival parameters remained undetectable as a result of the already very high therapeutic effect and low case number (OS and EFS: CHOP: 100% and 62.5% vs. R-CHOP: 90.9% and 87.0%; p = 0.3873 and p = 0.1702). Combining the standard CHOP treatment with rituximab resulted in a significant improvement of the therapeutic outcomes irrespective of the prognostic grouping. The data are comparable with those reported in the international literature.