A 28-year-old woman was admitted to our hospital with abdominal pain. Abdominal CT scan demonstrated a well-demarcated heterogeneous lipid tumor about 8 cm in diameter anterior to the stomach. Abdominal ultrasonography (US) revealed a low echoic mass without enhancement of vascular images. We made a diagnosis of the lipoma, but not excluding the possibility of a liposarcoma, or the torsion of a tumor. We performed an operation to remove the tumor. Finally the tumor was diagnosed as a lipoma of the lesser omentum with torsion of the pedicle. This is the third reported case of torsion of a lipoma. In addition, this case is considered as the first such case of lipoma of the lesser omentum.