The iliopsoas bursa is the largest bursa in the human body. Iliopsoas bursitis causes enlargement of the bursa and may lead to hip pain, groin mass, femoral nerve palsy, or compression of the femoral vein. We reported a case with the iliopsoas bursitis complicating old congenital dislocation of the hip. As not much yet known about the iliopsoas bursitis, it is sometimes misdiagnosed as abcess, inguinal hernia, aneurism, tumor, etc. Treatment is mainly conservative, but surgical treatment may be indicated in case of heavy groin pain or the compression and obstruction of adjacent structures.