Although hypophosphatemia is relatively uncommon, it may be seen in anywhere from 20% to 80% of patients who present to the ED with alcoholic emergencies, diabetic ketoacidosis (DKA), and sepsis. Severe hypophosphatemia, as defined by a serum level below 1.0 mg/dL, may cause acute respiratory failure, myocardial depression, or seizures. Because hypophosphatemia is not as often treated by ED physicians, becoming familiar with a single intravenous phosphate solution and specific guidelines for phosphate repletion are essential. One mL of the most commonly available phosphate solution (K2PO4) contains 4.4 meq of potassium and 3 mmol (93 mgs) of phosphate. Administering K2PO4 at a rate of 1 mL per hour is almost always a very safe and appropriate treatment for hypophosphatemia. This article provides guidelines for phosphate therapy in hypophosphatemic ED patients including those in DKA, those presenting with alcohol-related complaints including alcoholic ketoacidosis and patients with acute exacerbation of asthma and chronic obstructive pulmonary disease.