Background: Epstein-Barr virus (EBV) causes endemic Burkitt lymphoma (eBL). EBV control was improved by magnesium (Mg2+) supplementation in XMEN, an X-linked genetic disease associated with Mg2+ deficiency, high circulating EBV levels (viral loads), and EBV-related lymphomas. We, therefore, investigated the relationship between Mg2+ levels and EBV levels and eBL in Uganda.Methods: Plasma Mg2+ was measured in 45 women with low or high circulating EBV levels, 40 pediatric eBL cases, and 79 healthy children. Mg2+ uptake by T-lymphocytes was evaluated in samples from healthy donors.Results: Plasma Mg2+ deficiency (plasma level<1.8 mg/dl) was more likely in women with high-vs. low-EBV levels (76.0% vs. 35%; odds ratio [OR] 11.3, 95% CI 2.14-60.2), controlling for age, and in eBL cases than controls (42.0% vs. 13.9%; OR 3.61, 95% CI 1.32-9.88), controlling for sex, age group, and malaria status. Mg2+ uptake by T-lymphocytes was related to extracellular Mg2+ concentration.Interpretation: Plasma Mg2+ deficiency is associated with high EBV levels and eBL.