Liposarcoma is one of the most common soft tissue malignancies in adults, accounting for 15% to 20% of all sarcomas. We report a case of the largest dedifferentiated gastric liposarcoma recorded to date in a patient who presented with upper gastrointestinal bleeding. Initial pathology reports indicated a benign cause even after multiple biopsies were performed; only after surgical resection was the diagnosis confirmed. We discuss histopathology, genetic markers, and differential diagnoses.