Background <p>Fluorine-18 fluorodeoxyglucose positron emission tomography combined with multi-detector helical computed tomography (¹⁸F-FDG PET/CT) has emerged as one of the most important one of diagnostic and prognostic tools for lymphoma management. ¹⁸F-FDG PET/CT is well-regarded for evaluating bone marrow infiltration (BMI) and assessing disease burden in non-Hodgkin’s lymphoma patients. Therefore, this study was done to compare findings detected by ¹⁸F-FDG PET/CT with findings by bone marrow biopsy (BMB) regarding bone marrow infiltration (BMI) in patients had large B-cell lymphoma (LBCL).</p> Results <p>A cross-sectional study including 78 newly diagnosed cases of lymphoma who were referred for initial staging at first by BMB then underwent ¹⁸F-FDG PET/CT scan. Although 30 (38.5%) patients had bone marrow infiltration was detected by 18F-FDG PET/CT scan. However, 20 (25.6%) patients were detected by bone marrow biopsy. Both methods were concordant for BMI detection in 62 (79.5%) patients out of 78 cases with a Kappa value of 0.583 (<i>p</i> &lt; 0.001), indicating moderate agreement. Both of them revealed concordant negative results (57.69%), while concordant positive results (21.79%). The discordant result (16.67%) was BMB-negative but ¹⁸F-FDG PET/CT-positive. ¹⁸F-FDG PET/CT, had higher sensitivity and higher negative predictive value (85.0% and 93.8%), compared to BMB, which had (56.7% and 77.6%), respectively. While BMB had higher specificity and positive predictive value (93.8% and 85.0%) compared to ¹⁸F-FDG PET/CT (77.6% and 56.7%) respectively. The diagnostic accuracy was 79.5% for both two diagnostic methods.</p> Conclusion <p>¹⁸F-FDG PET/CT diagnostic imaging is more sensitive modality than bone marrow biopsy to detect bone marrow infiltration in patients with LBCL.</p>