A 53-year-old man presented with pain in the right hip. Radiological examination showed idiopathic osteonecrosis of the femoral head (ONFH) combined with a cam lesion. Findings on physical examination were consistent for femoroacetabular impingement. At surgery, we performed isolated arthroscopic correction for the cam lesion but did not use other treatment options such as hip arthroplasty or osteotomies for the ONFH. At the latest follow-up evaluation 3 years after surgery, findings indicted a satisfactory outcome, with a Harris hip score of 93.2 (compared with 76.4 before surgery), no joint-space narrowing, and no collapse of the femoral head. It is important to accurately diagnose the status of idiopathic ONFH and to consider another possible pathogenesis when a patient with idiopathic ONFH has hip pain even without femoral-head collapse.