Early exposure to oral erythromycin in young infants, particularly in the first 2 weeks of life, has previously been associated with the development of hypertrophic pyloric stenosis. We report a case of an infant who received an abbreviated 4-day course of oral erythromycin for suspected Chlamydia conjunctivitis at 5 days of life then underwent pyloromyotomy for pyloric stenosis less than 2 weeks later.