Objective To investigate causes and treatments for a fracture of the contralateral femoral neck in the elderly with prosthetic replacement for femoral neck fractures.Methods A retrospective analysis was conducted on 85 cases undergone prosthetic replacement for femoral neck fractures between March 2005 and May 2012,including 12 cases in secondary replacement group due to fractures of the contralateral uninjured femoral neck after primary prosthetic replacement and 73 cases in primary replacement group.Variables were compared between the two groups including causes of injury,age,sex,bone density,complications,quality of life,Harris score of the contralateral hip joint,surgical choice.Refracture reasons were evaluated and treatment plans were proposed.Results Immediate cause of injury in all cases was falling.Primary and secondary replacement groups showed mean age of (68.82 ± 5.18) yearsvs (76.83 ± 3.64) years (P＜0.05),male to female ratio of 0.66:1 vs 0.09:1 (P＜0.05),and bone mineral density of (0.507 ± 0.062) g/cm2 vs (0.461 ± 0.095) g/cm2(P ＜0.05).Moreover,cases in the two groups suffered from the associated complications (hypertension,diabetes mellitus,cataract,stroke,rheumatoid arthritis,and Parkinson' s disease).Except for the diabetes mellitus,incidence of the other five basic diseases presented significance differences between the two groups (P ＜ 0.05).Of primary and secondary replacement groups,quality of life was (76.26 ±14.17) points vs (67.86 ± 16.74) points (P ＜ 0.05) ; Harris score of the contralateral hip was (98.66 ±1.39) points vs (90.75 ± 5.39) points (P ＜ O.05).For treatment choice,32 total hip arthroplasty (THA) and 41 femoral head arthroplasty (FHA) with cement fixation in 44 cases and cementless fixation in 29 cases were performed in primary replacement group; two total hip arthroplasty and 10 femoral head arthroplasty with cement fixation in 11 cases and cementless fixation in one were performed in secondary placement group (P ＜ 0.05).Conclusions Fall remains the immediate cause of the contralateral fractures following prosthetic replacement of femoral neck fractures in the elderly.Aging,females,bone density reduction,high-incidence of complications,decreased quality of life,and joint function impairment after the primary prosthetic replacement are unfavorable factors.Prosthetic replacement is still the preferred choice of treatment and surgical procedure is more likely to be the simple cemented FHA.