Hypophosphataemia is a complication that may appear in undernourished patients who are given nutrition by either enteral or parenteral means. It is associated with several clinical manifestations, including cardiological, neurological and haematological conditions of note, and may potentially be even life-threatening. It is therefore mandatory to ensure prevention and follow-up in those patients at risk of suffering this condition, taking into account the considerable morbidity and mortality associated with it.