ABSTRACT We evaluated the predictive value of I-PET after one course of chemoimmunotherapy in patients with newly diagnosed DLBCL. 112 DLBCL patients were enrolled. All patients had PET/CT scans performed after one course of chemotherapy (PET-1). I-PET scans were categorized according to International harmonization project criteria (IHP) and to Deauville 5 point scale (D 5PS) with scores 1-3 considered negative (D 5PS>3) and D 5PS with scores 1-4 considered negative (D5PS=5). Ratios of tumorSUVmax to liverSUVmax were also analyzed. We found no difference in progression-free survivals (PFS) between PET-negative and PET-positive patients according to IHP and D 5PS>3. The 2-year PFS using D 5PS=5 was 50.9% in the PET-positive group and 84.8% in the PET-negative group (p=0.002). A tumor/liver SUVmax cut-off of 3.1 to distinguish a D 5PS scores of 4 and 5 provided the best prognostic value. PET after one course of chemotherapy was not able to safely discriminate PET positive and PET negative patients in different prognostic groups.