Infantile hypertrophic pyloric stenosis (IHPS) is the most common reason for nonbilious vomiting in infants. Its cause is unknown. Hypertrophy of pyloric muscle can progress after birth and reach complete gastric outlet obstruction. Usually symptoms start after the age of 3 weeks. In the past diagnosis was based on history of projectile, nonbilious vomiting and palpation of a pyloric mass. Greater awareness of IHPS and increased use of imaging modalities, mainly abdominal ultrasonography, have resulted in a change in the clinical condition at presentation. The length of illness before admission has decreased and weight loss, dehydration and metabolic abnormalities have become less common. We describe an atypical clinical manifestation of IHPS: bilious vomiting. This atypical presentation may be due to earlier diagnosis.