Thirteen cases of progressively aggravated hip pain after artificial bipolar femoral head replacement have been treated surgically for the second time since June 1989. Based on the findings of radiographs and observations on re-operation, the hip pain is considered to be multifactorial and probably related to the following points: (1) Joint loosening, which may be due to unstability of the prosthesis, an increase in friction, fatigue arising from the difference in mechanical nature between the prosthetic stalk and the femoral shaft, the amount of the particles around the stalk failed to fix the implant, and local bone atrophy. (2) Abrasion or penetration to the femoral cortex, which may be due to the significant difference in friction coefficient between the prosthetic articular surface and human acetabulum, the development of shear force on the joint surface and the stress focused on the outer cortex. (3) Bone cell proliferation and the articular capsule osteolysis, which is believed to be due to unsuitable use of prosthesis. Malfixation of the bipolar femoral head plays an essential role in the hip loosening and pain at the early stage after operative intervention