Hydatid cyst of liver is a disease usually seen in endemic regions. While it is very small at the beginning, cyst diameter increases approximately 1-3 cm per year. Among known complications of hydatid disease, pressure to the adjacent organs due to the cyst growth, perforation into peritoneal cavity or bile truct are most noteable. However, its fistulization into gastrointestinal tract is very rare. A 80-year-old male patient presented with the complaints of abdominal pain, fever and deterioration in general physical condition. It was determined that the patient was diagnosed with hydatid cyst of liver about 15 years ago but refused treatment. Imaging revealed a 20x15 cm multiseptal cystic lesion filled with air in the right lobe of liver. Patient was admitted to OR and exploration revealed that cyst had fistulized into the duodenum. The fistulization of liver hydatid cyst into the duodenum is very rare. We believe that the size of cyst and the delay in treatment caused the cystoduodenal fistula.