Omental and mesenteric cysts are rare intra-abdominal masses in the pediatric population. When large, these lesions can mimic large-volume ascites and may not be immediately recognized. This can lead to a delay in appropriate treatment as a result of additional unnecessary tests and procedures. We present a case of a large omental cyst in an 18-month-old male with emphasis on imaging findings that can help diagnose this rare, but important entity.