Myofibroma is a rare benign tumor typically occurring in the skin and subcutaneous tissues of the head and neck in infants and young children. The incidence of solitary intraosseous and adult myofibroma is extremely low. Although there have been a few reported cases of solitary intraosseous myofibroma in adult patients, most of these cases involved the craniofacial bones. We present the case of a 64-years-old woman presenting with minimal pain of the right buttock and groin. Radiographs and computed tomography showed a huge tumor spreading around the ilium, and non-uniform calcifications were noted inside the tumor. Iliac tumor biopsy was conducted, and intraosseous myofibroma was suspected. We performed surgical resection of the mass, and a final diagnosis of myofibroma with metaplastic bone production was made. We have presented an extremely rare case of solitary intraosseous myofibroma in an adult patient. Copyright © 2017 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.