Spontaneous, severe, acute hypophosphataemia is an unusual finding in dogs. This case report describes the presentation of a seven-year-old Greyhound with an acute history of polypnoea. Clinical examination revealed an increased rectal temperature, congested mucous membranes, pain on flexion of the right hindlimb and muscle fasciculations. Haematology and plasma biochemistry were generally unremarkable apart from severe hypophosphataemia and a markedly increased creatine kinase concentration. The hypophosphataemia was treated with an intravenous infusion of Toldimphos sodium, which is an organically combined phosphorus preparation. The hypophosphataemic state was rapidly corrected and clinical signs resolved over the following five days. The cause of the severe hypophosphataemia was unclear. This case demonstrates that severe, acute hypophosphataemia can be successfully treated with Toldimphos sodium infusion with a good long-term outcome even in dogs that are initially presented with debilitating clinical signs.