The incidence of Hypertrophic pyloric stenosis (HPS) in premature infants is rare, the presentation is not typical, and the diagnosis delayed due to uncertain diagnostic criteria in abdominal ultrasonography (US). We report two premature infants with HPS diagnosed by US and upper gastrointestinal (UGI) contrast study. Patient 1. A premature female infant (birth weight 1950 gm at 34 week's gestation) with the onset of intermittent vomiting at 9 days of age was evaluated. US was normal at 13 days of life, however, abnormal at 41 days of life (pyloric muscle length 16.5 mm). Patient 2. A premature male infant (birth weight 1470 gm at 29 week's gestation) with the onset of intermittent vomiting at 10 days of age was evaluated. US showed pylorospasm at 11 days of life, however, findings compatible with HPS at 57 days of life (pyloric muscle thickness 11 mm).UGI contrast study at 48 days of life showed similar findings in both cases. Both patients had undergone pyloromyotomy. In conclusion, the diagnosis of HPS in premature infants requires careful follow-up by US and UGI contrast study.