The paper deals with the advantages of ultrasound diagnosis of hypertrophic pyloric stenosis in newborns. Ultrasound decreases the number of radiological examinations of gastroduodenum and reduces diagnostic exposure of children to X-rays. In the last three years 107 children had manifested clinical signs of hypertrophic pyloric stenosis. The ultrasound studies revealed hypertrophic pyloric stenosis in 55 patients (51.4%). There were 48 boys (87.3%) and 7 girls (12.7%). Patients were aged 17 to 75 days (average about 40 days). The sonogram finding was typical for hypertrophic pylorus, which made the diagnosis easier. There were no false positive or false negative ultrasound findings. All patients with hypertrophic pyloric stenosis were operated on and diagnosis was confirmed. Ultrasound is reliable in diagnosis of hypertrophic pyloric stenosis. Ultrasound examination is technically easy and fast, what is important for urgent surgical therapy. In children with persistent projectile vomiting, suspected of hypertrophic pyloric stenosis, ultrasound is the method of choice and should replace X-ray examinations.