Hypophosphataemia is defined as a phosphate level of less than 2.5 mg/dl (0.8 mmol/l). Many of the pathophysiological changes and therapeutic interventions in the first week post-burn affect serum phosphorus concentration. A retrospective study reviewed the medical records of nine severely burned patients, and a special reference of decreased phosphate serum level was noted. Serum phosphorus levels declined, with a nadir between days 2 and 6 post-burn. The severe hypophosphataemia that often follows major burns returns to normal phosphorus levels on days 18 to 20 post-burn. Weight-based phosphorus dosing is safe to use in critically burned patients receiving nutritional support. Moderate doses effectively increase serum phosphorus concentrations.