A 17-year-old male with a past medical history significant for asthma and gastrointestinal reflux disease presented with a 1-week history of intermittent abdominal pain, nausea, bilious emesis, and bloody diarrhea. Physical examination revealed periumbilical and right lower quadrant tenderness without peritoneal signs. Laboratory tests showed a white blood cell count of 11,500 cells/mm3 with 31% eosinophils (the absolute eosinophil count was 3,600/mm3). A stool test for ova and parasites was negative. Quantitative immunoglobulins were normal. Serology for Toxocara and human immunodeficiency virus were negative. Strongyloides antibodies were equivocal. erythrocyte sedimentation rate (ESR), antinuclear antibody (ANA), and anti-neutrophil cytoplasmic antibody (ANCA) antibodies were normal. Ultrasound examination performed at the time of admission revealed moderate ascites, dependent in the right lower and upper abdominal quadrant. Computerized tomography (CT) of his abdomen demonstrated thickening of the terminal ileum and ascites. No free air in the abdomen was noted. The ascitic fluid was aspirated under CT guidance and sent for cytological evaluation. A hepatobiliary iminodiacetic acid scan to track the flow of bile was normal. An esophagogastroduodenoscopy (EGD) and colonoscopy with mucosal biopsies were performed, which showed a notable increase in esophageal eosinophils, but no colitis. This was followed by laparoscopic examination to obtain small bowel serosa and mesenteric biopsies. During laparoscopy, petechiae were identified on the serosa of the ileum. Following a diagnosis of eosinophilic ileitis with associated eosinophilic ascites (see below), intravenous steroid treatment was started. The patient responded very well to therapy and was discharged on oral prednisone, which was eventually tapered and stopped. A follow-up ultrasound of the abdomen demonstrated virtually complete resolution of his intraabdominal fluid. Straw-colored ascitic fluid was obtained and submitted to both the cytopathology laboratory in Cytolyt and the hematology laboratory. Fluid analysis [] was remarkable for 65% eosinophils. ThinPrep slides were stained with a Papanicolaou stain, a cytospin with a Wright-Giemsa stain, and a cell block was prepared and stained with hematoxylin and eosin. The peritoneal fluid revealed an abundance of mature eosinophils [] present in a bloody background. Malignant cells or microorganisms were not identified. Microbiology cultures of the ascitic fluid were negative for bacteria, mycobacteria, and fungal organisms. Multiple gastrointestinal biopsies were obtained as described above. Occasional intraepithelial eosinophils were present in the proximal and distal esophageal mucosa. Gastric and colorectal biopsies did not show increased eosinophils. However, within the ileum, there were numerous eosinophils present in the muscularis propria and the serosa [], diagnostic of eosinophilic enteritis. A mesenteric lymph node demonstrated reactive lymphoid hyperplasia with numerous sinusoidal eosinophils and associated Charcot-Leyden crystals.