Approximately 30 patients with familial hypomagnesemia-hypercalciuria have been reported. We describe an 8-year-old girl with cardinal findings of familial hypomagnesemia-hypercalciuria (hypomagnesemia, hypermagnesiuria, hypercalciuria, renal insufficiency, hyperuricemia, elevated serum parathormone, hyposthenuria and nephrocalcinosis), who received combination therapy consisting of magnesium salts, thiazide diuretic and potassium supplementation. At the 4-year follow-up investigation under this treatment, the patient was found to have cerebral pseudotumor (increased intracranial pressure with normal or small ventricles on neuroimaging, no evidence of an intracranial mass and normal cerebrospinal fluid composition) with papilledema and visual field defects. Thiazide therapy was terminated and the cerebral pseudotumor disappeared. The authors hypothesize that cerebral pseudotumor in this patient was related to severe hypocalcemia, as a consequence of profound hypomagnesemia induced by protracted thiazide treatment. To our knowledge, this is the first report of a child with familial hypomagnesemia-hypercalciuria who developed pseudotumor cerebri after thiazide therapy.