Fifteen of 18 cases who underwent conversion total hip prosthesis due to painful hemiarthroplasty, between 1992 and 1997, were investigated retrospectively. The 13 (86.6%) women and two (13.4%) men (mean age, 59 years) were followed up for an average of 32 months. Pre-operative and post-operative Harris hip scores were 36.4 (28 - 42) and 85.9 (69 - 98), respectively. In all cases the femoral component had more than 2 mm radiolucency in Gruen zones I, IV and VII, and five cases had acetabular protrusion; other cases had cartilage erosion. In the last follow-up of conversion total hip prosthesis, there was no radiolucency in either femoral or acetabular components. Comparing our results of conversion total hip prosthesis with primary total hip prosthesis results for femoral neck fractures in the literature we conclude that, in elderly patients with femoral neck fractures, primary total hip prosthesis has better results.