Hypertrophic pyloric stenosis can be diagnosed accurately by physical examination alone. However, ultrasonographic confirmation is obtained in the majority of cases, often before clinical evaluation by the surgeon. The present study examines whether the easy access to ultrasonography by the primary physician has affected the care of infants with pyloric stenosis. During a 24-month period, 100 infants were treated for pyloric stenosis at the authors' institution. There were 78 boys and 22 girls; the age range was 9 to 90 days (median, 30.0 days). The children were referred for surgical evaluation, but abdominal ultrasonography was ordered concomitantly (or within 1 hour of surgical consultation) in all cases. The median age at the onset of the first symptoms was 24.0 days. The time between onset and hospital admission was less than 7 days for 72 patients, and more than 2 weeks for seven. Metabolic alkalosis or acidosis, hypokalemia, hypochloremia, and dehydration were noted in 10%, 5%, 3% and 9%, respectively. Six infants had prolonged pre- and postoperative courses, because of prematurity (4) or associated conditions (2). For the remaining patients, total hospitalization period and postoperative stay were 3.8 +/- 0.9 days and 2.8 +/- 0.6 days, respectively. Although the diminished importance of clinical skills in the diagnosis of pyloric stenosis may be regrettable, the availability to the primary care physician of this easy, safe, inexpensive, and reliable imaging modality may contribute to prompter treatment. The patients were hospitalized, with a correct diagnosis, within days of the appearance of the initial symptoms. Because so little time had elapsed, water and electrolyte imbalances were not present, and the patients could be operated on within hours of admission.