Nine hips in eight patients had development of femoral endosteal cortical erosion after a cementless total hip arthroplasty. Serial anteroposterior and lateral radiographs of all of the affected femora were reviewed to determine the interval between the operation and the first recognition of the osteolytic lesion or lesion, as well as to evaluate the radiographic appearance and progression of the lesions. We reviewed the one hundred twenty hips in one hundred eleven patients had a cementless total hip arthroplsty at the department of Orthopaedic Surgery, Pusan National University Hospital from January 1985 to December 1991. The mean average follow up period was forty five months (twenty four to one hundred nine months). Osteolysis was first noted radiographically at forty four to eighty five months(mean, sixty three months) postoperatively; it occurred most frequently around the distal portion of the prosthetic stem. Three of the femoral components were shown to be loose. The remaining six hips had been judged to be stable when the endosteal erosion had first been identified. The osteolysis was more severe in the femora in which the component was loose than in those in which it was stable. Of the six stable hips and two unstable hips except revised one hip, who were followed, four hips had an increase in the size of osteolytic lesion with time. All two unstable hips and two stable hips among six stable hips had an increase in the size of osteolytic lesion with time. Therefore, close follow up in necessary for patients in whom osteolysis develops in association with a stable cementless femoral component.