Objective: To evaluate the association between serum magnesium levels below 1.5 mg/dL and the development of stage I pressure ulcers in hospitalized patients. Methods: A retrospective observational study was conducted in 200 hospitalized patients at Hospital General de Xoco. Patients over 18 years old with reduced mobility and a hospital stay of at least 7 days were included. Hypomagnesemia was defined as serum magnesium levels below 1.5 mg/dL. A multivariate logistic regression analysis was performed to adjust for comorbidities. Results: Of the total patients, 57% developed stage I pressure ulcers. Patients with hypomagnesemia had a significantly higher risk of developing ulcers (OR = 11.1 p < 0.001). Peripheral venous insufficiency (OR = 2.63 p = 0.028) and diuretic use (OR = 2.83 p = 0.014) were associated with a higher risk of developing ulcers. Male sex was associated with a lower risk (OR = 0.42 p = 0.022). Conclusion: Hypomagnesemia is an important risk factor for the development of pressure ulcers in hospitalized patients. Monitoring magnesium levels may help prevent these complications.