Introduction: Follicular lymphoma (FL) is an indolent yet heterogeneous B-cell lymphoproliferative disorder. Most people respond to treatment well. However, a particular group of patients has a poor prognosis, and these patients are difficult to define.Patients and methods: We retrospectively analyzed FL patients treated at the University of Debrecen in the past 20 years. We investigated prognostic factors that may influence the survival of FL patients.Results: We found a standardized uptake value (SUV)max cut-off value of 9.85 at the staging PET/CT to significantly separate FL patients’ progression-free survival (PFS) (p=0.0003, HR: 0.2560, 95%CI: 0.1232-0.5318). Lymphocyte/ monocyte (Ly/Mo) ratio of 3.45 drawn at diagnosis also significantly predicted PFS (p=0.0324, HR: 1.806, 95% CI: 1.051-3.104). Combining patients’ with staging SUVmax >9.85 and Ly/Mo < 3.45 a high-risk group of FL patients can be identified (p<0.0001, HR: 0.1033, 95%CI: 0.03719-0.2868). Similarly, a significant difference was shown with a SUVmax cut-off of 3.15 at the interim PET/CT (p<0.0001, HR: 0.1535, 95%CI: 0.06329-0.3720). Combining patients with staging SUVmax >9.85 and interim SUVmax >3.15, a high-risk group of FL patients can be identified (p<0.0001, HR: 0.1037, 95%CI: 0.03811-0.2824). The PFS difference is translated into overall survival advantage (p=0.0506, HR: 0.1187, 95%CI: 0.01401-1.005).Discussion: Biological prognostic factors, such as the Ly/ Mo ratio, may improve the prognostic assessment of staging PET/CT. Nevertheless, PFS difference is translated into OS when using a combination of staging and interim SUVmax. We consider investigating additional biological prognostic factors while currently highlighting PET/CT's role in FL.