Hyponatremia is common in preterm infants. The causes are usually related to the inability of the premature kidneys to excrete a given water load, excessive sodium losses, or inadequate sodium intake. Here, we present a case of severe hyponatremia in an extreme preterm infant, associated with the use of aminophylline. Aminophylline was administered intravenously on day 1 for the treatment of apnea of prematurity. On day 3, the patient developed hyponatremia which was not responsive to sodium replacement and fluid restriction. Due to concerns of aminophylline-induced hyponatremia, aminophylline was discontinued on day 6, and within 48 h of discontinuation, serum sodium normalized without the need for sodium supplementation. The purpose of the case report is to present a rare complication associated with aminophylline use and to shed light on potential deleterious effects associated with drug shortages.