Introduction: The Unicameral Bone Cyst (UBC) is a benign osteolytic lesion primarily found in the metaphyseal part of long bones in children. It is important as it can involve growth plate involvement, cause pathological fractures and deformities of the affected limb. We report this case to emphasize that hip area pathologies can be represented with knee pain and discomfort. 
Case Presentation: The patient was a 9-year-old girl with a bone cyst in the right proximal femur, with functional knee pain and limping. The diagnosis was made after two years of pain in the knee area. As the cyst was symptomatic and the signs of impending pathological fracture were seen, the lesion was managed by curettage and fibular strut allograft and proximal humerus locking plate.
Conclusions: The patient has been examined for knee joint problems for a long time, and her femur bone cyst was diagnosed after two years of pain. However, it could become a pathologic fracture or involve the growth plate and stop the limb’s growth, thus affecting the patient’s quality of life. Therefore, in children with chronic knee pain, careful assessment of the hip area is recommended.