Jacquelyn K. Patterson, MD1, Mackenzie Esch, MD1, and John R. Stephens, MD1 Case A 6-week-old Hispanic girl presented with 1 week of nonbloody, nonbilious vomiting. Emesis was large volume and occurred with every feeding. The patient had a history of poor weight gain. She was initially breastfed, but after the onset of emesis, parents tried formula thickened with rice cereal with no improvement. The patient had no diaphoresis with feeds, appeared to have a good appetite, and was voiding normally. Parents did report several loose stools in the preceding week. Her past history was remarkable only for a normal vaginal delivery at 37 weeks and hospitalization for respiratory syncytial virus bronchiolitis at 2 weeks of age. The patient’s weight was 3.26 kg (