Severe hypophosphataemia is a well known metabolic disturbance, potentially serious. Clinicians are not always aware of this condition, which most likely is missed sometimes. We present a case in which severe hypophosphataemia was an important part of the clinical picture. An alcoholic was hospitalized because of epigastric pain, nausea and poor health. Seven days after admission he still was very weak and somnolent. He did not eat, and developed urinary retention due to paresis of the bladder. An extremely low level of s-phosphate, 0.12 mmol/l, was discovered the seventh day. The next two days he was substituted with 60 mmol phosphate i.v. At the same time his general condition improved dramatically. We believe that severe hypophosphataemia was an important cause of the persistently poor clinical condition of our patient. Finally, we present the causes of hypophosphataemia, stressing that serum phosphate does not always reflect total body phosphate. We discuss the possible manifestations of hypophosphataemia, and we give practical advice on treatment.