This report presents the unusual case of a 5-year-old girl with iliac fracture just after Salter innominate osteotomy for developmental dysplasia of the hip. The iliac fracture was diagnosed two days after Salter innominate osteotomy, and computed tomography (CT) revealed that it was at the extremely thin portion of the iliac wing called the “iliac fossa.” We were able to reduce the fracture by pulling the left leg distally, and after reducing the iliac bone, the ilium was fixed by Kirschner wire from the anteroinferior iliac spine and anterosuperior iliac spine. The patient was in a hip-spica cast for 6 weeks postoperatively and allowed to walk from 3 months after the surgery. At the last follow-up one year after the surgery, bone union was completely obtained, and she had no complications. The cause of the fracture seems to be the stress concentration on the iliac fossa due to the cranked iliac osteotomy line passing through the iliac fossa. The current case indicates the importance of careful evaluation by CT before surgery and ensuring that the osteotomy line does not extend near the iliac fossa.