To investigate whether magnesium abnormalities are associated with the administration of magnesium-containing laxatives in a palliative care setting, we measured the serum magnesium levels in 48 patients with advanced cancer at our palliative care unit (PCU). The mean magnesium concentration in all patients was 2.09 mg/dl (confidence interval [CI], 1.38-3.62). Patients receiving magnesium-containing laxatives (n=38) showed significantly higher serum magnesium concentrations than patients without laxatives (n=10) (2.17 mg/dl vs 1.8 mg/dl, p=0.006). Although 10 patients had serum magnesium abnormalities (hypomagnesemia, 8 and hypermagnesemia, 2), we did not observe clinical manifestation associated with magnesium abnormalities. Interestingly, neither the duration nor the dose of laxatives correlated with serum magnesium concentration. Overall, patients at the PCU tend to have magnesium abnormalities and their symptoms may be analogous to those of advanced cancer patients; in particular, terminal patients with such symptoms might be considered to have magnesium abnormalities.