Necrotizing gastritis is a rare pathology causing a high rate of morbidity and mortality in the infants. A 4-week-old baby, with right hypoplastic kidney and ectopic ureter, was admitted because of profound septic shock and "coffee ground" vomitus. Aggressive treatment was started and hemodynamic stabilization was achieved. On the fourth admission day, ascites was noted and on the eighth day in a plain abdominal x-ray, free air was shown. At urgent explorative laparotomy, double posterior gastric wall perforations with extensive gastric wall necrosis were found, which required subtotal gastrectomy. The etiology and pathophysiology of this rare process are discussed with an emphasis on the difficulty in diagnosis of posterior gastric perforation into the lesser sac.