Hypertrophic pyloric stenosis (HPS) is rare in premature infants. We report a case of HPS in an extremely low birth weight neonate (28 weeks of gestation, 622 gr), discovered on the 10th week of life. Although the diagnosis and treatment of pyloric stenosis has ben well established for many years, the presentation in preterm babies is atypical and the diagnosis often delayed. A brief review of literature is included.