Treating patients with DLBCL remains a challenge, as the response to first-line immunochemotherapy is somewhat unpredictable. The International Prognostic Index (IPI) is one of the most widely used methods for assessing prognosis. Interim PET/CT (iPET/CT) can play an important role in the early identification of 'non-responder' patients before the end of treatment examination. In this study, we retrospectively analyzed 104 newly diagnosed DLBCL patients treated with R-CHOP-like regimens who underwent iPET/CT imaging during therapy. There was a significant difference in 2-year OS between patients with negative iPET/CT and those with positive iPET/CT. Patients who had positive iPET/CT showed inferior 2-year PFS compared to those with negative iPET/CT. According to IPI, there was a statistically significant difference in 2-year OS and PFS between patients in the lower and higher risk groups. However, these patients can be further subdivided according to iPET/CT. The iPET/CT results in the present study clearly separate good- and poor-prognosis patients according to differences in 2-year OS, both in the lower and higher IPI risk groups. These results are in agreement with those of previous studies that demonstrated that iPET/CT has high negative predictive value, clearly identifying good-prognosis patients even within the poor-prognosis IPI group.