INTRODUCTION: The incidence of Cryptosporidial enteritis (CE) has recently risen in the USA due to water and foodborne outbreaks. It has a self-limited course in healthy hosts. We describe a case of a healthy female with history of gastric bypass surgery who presented with a one-month history of voluminous watery diarrhea and vomiting. This was a rare case of CE diagnosed by endoscopic biopsies of two anastomotic peptic ulcers that were colonized by Cryptosporidium spp. CASE DESCRIPTION/METHODS: 57-year-old female with a history of GERD, iron deficiency anemia, and Roux-en-y gastric bypass complicated by jejunal strictures with revision of the gastro-jejunal anastomosis, presented with a 7-day history of vomiting and crampy epigastric abdominal pain. She recently returned from a two-week vacation to Latin America. Upon arrival, she experienced progressively worsening voluminous watery diarrhea associated with intermittent melanotic stools followed by frequent episodes of non-bilious, non-bloody vomiting along with reduced oral intake. Abdominal exam revealed hyperactive bowel sounds with tenderness to deep palpation of the epigastrium. Her hemoglobin dropped from a baseline of 11.2 g/dL to 9.1 g/dL. CT scan of the abdomen with contrast showed inflammation around the gastro-jejunostomy site. Blood and stool cultures were negative. Upper endoscopy revealed a 1 cm and 2 cm clean-based ulcers with a deep crater at the anastomotic site. Biopsy demonstrated spherical bluish-purple organisms, 2-5 µm in diameter on hematoxylin and eosin, Gomori Methanamine Silver Nitrate and Masson's trichrome stains. They were suggestive of Cryptosporidium, and the patient was diagnosed with CE. Patient's immunodeficiency workup was unremarkable. Patient's symptoms resolved with a three-day course of Nitazoxanide 500 mg twice per day. DISCUSSION: CE is a significant cause of chronic diarrhea in both healthy and immune-compromised individuals, thus stands as a key differential in those presenting with persistent voluminous diarrhea. The modified acid-fast stain carries only 50% sensitivity to this protozoan, and diagnosis is often missed on routine stool ova and parasite tests. Novel diagnostic modalities have proven useful in identifying this protozoan in stool samples. We report the first case documenting Cryptosporidium colonization of anastomotic site peptic ulcers with complete resolution of symptoms following a short course of Nitazoxanide.