A 75-year-old woman was admitted with febrile confusion and abdominal pain. She was taking medications that included lanthanum carbonate. Examination, biology, a cerebral scan, and a review of her medications could not explain the confusion. The plain film of the abdomen revealed multiple diffuse calcium-like deposits throughout the digestive tract. The plasma levels of lanthanum were higher than normal. The confusion resolved after discontinuation of the lanthanum carbonate. This case raises the problem of the potential role played by lanthanum tablet residue in the genesis or aggravation of diverticular flare-up and the problem of the potential permeability of the blood-brain barrier with lanthanum use in case of its digestive accumulation, leading to increased serum concentrations.