Hypophosphatemia occasionally underlies neurological disorders such as encephalopathy, myopathy and neuropathy. Although several cases have been reported in the literature, severe hypophosphatemia as a cause of neurological disorders is rarely mentioned in neurological textbooks and is seldom thought of in practice. We present a 69-year-old woman who develops encephalopathy and rapidly progressive weakness due to hypophosphatemia. The cause of hypophosphatemia is often iatrogenic and multifactorial. Signs and symptoms are mostly non-specific, thus complicating correct diagnosis and appropriate treatment.