PURPOSE: To evaluate the ultrasonographic findings of abdominal wall endometrioma. MATERIALS & METHODS: The ultrasonographic findings and clinical findings were retrospectively evaluated in 12 patients with abdominal wall endometrioma. Ultrasonographic examination was preoperatively performed with 7.5MHz linear sector scanner and endometriomas were all treated by surgical excision. Ultrasonographic findings of endometrioma were evaluated focused on 1) location of mass, 2) size, 3) shape, 4) boundary, 5) internal echo and 6) posterior echo change. RESULTS: The mean age of patients was 34 years(range: 28-42). All endometriomas were palpated near the C-section scar on physical examination. Most of masses (9 cases) confined to subcutaneous tissue and the remaining 3 cases were within the rectus sheath. The size of masses ranged from 1.5 to 4.5 cm (mean 2.7cm) and their shape all appeared round to ovoid. Their boundaries were relatively well-defined in 7 cases and ill-defined in 5 cases. All masses showed heterogenous hypoechoic internal echogenicity relative to surrounding tissue and no posterior echo change besides one mass with cystic portion. CONCLUSION: Most common findings of abdominal wall endometrioma were heterogenous hypoechoic mass without posterior echo change. Abdominal wall endometrioma should be firstly considered for differential diagnosis in cases that heterogenous hypoechoic mass is found near the C-section scar in the premenopausal women.