Jamie is a 3-month-old female who presents with her mother for evaluation of “throwing up.” Mom reports that Jamie has been throwing up pretty much all the time since she was born. Jamie does not seem to be sick. In fact, she drinks her formula vigorously and often acts hungry. Jamie has normal soft brown bowel movements every day and, overall, seems like a happy and contented baby. She smiles readily and does not cry often. Other than the fact that she often throws up after drinking a bottle, she seems to be a very healthy, happy infant. A more precise history suggests that Jamie does not exactly throw up—she does not heave or act unwell—but rather it just seems that almost every time she drinks a bottle she regurgitates a milky substance. Mom thought that she might be allergic to her formula and switched her to a hypoallergenic formula. It didn’t appear to help at all, and now Mom is very concerned.