Abstract: Objective To investigate the diagnostic value of ¹⁸F-FDG PET/CT in bone marrow which appears high metabolism. Methods 62 ¹⁸F-FDG PET/CT image cases were analyzed from July 2010 to June 2015 in our hospital, which bone marrow showed diffuse high metabolism, and the remaining parts of the image presented no malignant metabolic. PET, CT and PET/CT fusion images were compared with the pathology or follow-up results, respectively. Results The PET/CT images of 62 patients showed diffuse increase in FDG uptake of whole-body bone and bone marrow system, in the spine, sternum, ilium as the significant. The CT abnormality was 9 cases, which showed a diffuse increase or decrease of bone density. Pathological examination showed benign lesions was 35 cases and reactive bone marrow hyperplasia was found in 15 cases, bone marrow hyperplasia roughly normal in 14 cases, bone marrow hyperplasia slightly active in 6 cases. Malignant lesion was found in 27 patients, including lymphoma bone marrow involvement in 14 cases, different types of leukemia in 11 cases, MDS in 2 cases. The SUVmax of malignant lesion was (7.2±2.4), which was more than (5.2±1.8) of benign groups (t was 3.89, P was 0.000), and the difference was statistically significant. According to the SUVmax to get ROC curve, the area under the curve was 0.757, P was 0.001. When Youden Index was max (0.532), SUVmax was 6.25. Using 6.25 as the threshold value, for 18F-FDG PET/CT showing high metabolism with bone marrow, in these 62 cases, the sensitivity, specificity and accuracy of PET in differential diagnosis of benign and malignant were 70.4%, 82.9% and 77.4%. Conclusions PET has a considerable clinical value for early diagnosis of bone marrow malignant lesions, and it is worthy of further biopsy of bone marrow in PET diffuse high metabolic lesions.