<p>Disorder of the immune microenvironment plays an important role in the occurrence and development of multiple myeloma in patients. While bone marrow SUVmax on ¹⁸F-FDG PET/CT correlates with MM disease characteristics, its association with the immune microenvironment remains unclear. This study analyzed 49 newly diagnosed MM patients, dividing them into high and low SUVmax groups based on bone marrow ¹⁸F-FDG uptake. Differences in clinical characteristics, laboratory indicators, lymphocyte subsets, and cytokines were examined. Additionally, the correlation between SUVmax and these parameters was assessed. Results showed that patients with high SUVmax had a heavier disease burden, including a greater proportion of advanced-stage disease, more pathological fractures, and increased bone marrow plasma cell percentage. The high SUVmax group also exhibited a more immunosuppressive microenvironment, with a reduced proportion of CD4⁺ T cells and increased levels of regulatory T cells (Tregs) and cytokines such as IL-4 and IL-10. Correlation analysis indicated that the SUVmax of ¹⁸F-FDG uptake was positively correlated with the proportion of Treg cells and the concentrations of cytokines such as IL-4, IL-6, and IL-10, while negatively correlated with the proportion of CD4⁺ T cells.After adjustment for bone marrow plasma cell percentage, high SUVmax remained associated with decreased CD4⁺ T cells and increased Treg cells. This study suggests that bone marrow SUVmax is associated with both disease burden and immune microenvironment status in MM patients, which may provide valuable insights for disease assessment and treatment.</p>