Introduction: Pyloric thickness of 3 mm or higher and length of 15 mm or higher by ultrasonography (US) is widely accepted as diagnostic criteria for pyloric stensosis (PS). However, infants presenting at earlier ages are held to this same criteria, which may not be applicable. Methods: Retrospective review was conducted on patients evaluated with pyloric US to rule out PS from May 2010 through December 2010. Pearson correlation was used to detect an association between weight and age with pyloric thickness and length. Sensitivity and specificty for US parameters were determined. Results: Three hundred four patients underwent 318 ultrasounds, of which 67 had PS. Of those with PS, age and weight had a positive correlation with thickness (P < .007), and age positively correlated with length (P < .001). In patients with and without PS, there was a negative correlation for both age and weight with thickness (P < .02). Those who did not have PS held a stronger negative correlation between age and thickness (P = .002). Overall, US had a 100% sensitivity and specificity for PS. Thickness of 3 mm or higher was 100% sensitive and 99% specific, and pyloric length of 15 mm or higher was 100% sensitive and 97% specific. Conclusions: Although significant associations between age and weight with pyloric thickness and length may exist, our data indicate that this does not have an impact on the diagnostic criteria for PS. © 2012 Elsevier Inc. All rights reserved.