Knee joint pain is one of the most common complaints related to the skeletal system encountered by paediatricians. Knee joint pain generally occurs as the result of hypermobility and growing pains, though disorders manifesting as arthritis/arthralgia and orthopaedic problems should be considered in the differential diagnosis. A thorough and careful physical examination and laboratory and radiological findings are of importance for an accurate diagnosis. Although treatment should be based on the aetiology of the knee pain, non-steroid anti-inflammatory drugs can be used to alleviate the pain. A 7-year-old male patient presented with recurring pain in the left knee. Physical examination of the patient, laboratory tests, and radiological examination of the knee joint were normal; roentgenograms performed for a presumed hip joint problem revealed a focal cortical defect on the left femoral head and an increased effusion in the left hip joint space compared with the right counterpart. With this case report, we would like to highlight that paediatric health and diseases specialists (paediatricians) should consider hip joint pathologies when patients present with knee pain, particularly knee pain with an unidentified aetiology.