Summary The aim of this study was to determine the total medical costs for treating displaced femoral neck fractures with hemi-or total hip arthroplasty in fit elderly patients. The mean total costs per patient at 2 years of follow-up were €26,399. These results contribute to cost awareness. Introduction The absolute number of hip fractures is rising and increases the already significant burden on society. The aim of this study was to determine the mean total medical costs per patient for treating displaced femoral neck fractures with hemi-or total hip arthroplasty in fit elderly patients. Methods The population was the Dutch sample of an international randomized controlled trial consisting of femoral neck fracture patients treated with hemi-or total hip arthroplasty. Patient data and health care utilization were prospectively collected during a total follow-up period of 2 years. Costs were separated into costs for hospital care during primary stay, hospital costs for clinical follow-up, and costs generated outside the hospital during rehabilitation. Multiple imputations were used to account for missing data. Results Data of 141 participants (mean age 81 years) were included in the analysis. The 2-year mortality rate was 19 %. The mean total cost per patient after 10 weeks of follow-up was €15,216. After 1 and 2 years of follow-up the mean total costs were €23,869 and €26,399, respectively. Rehabilitation was the main cost determinant, and accounted for 46 % of total costs. Primary hospital admission days accounted for 22 % of the total costs, index surgery for 11 %, and physical therapy for 7 %. Conclusions The main cost determinants for hemi-or total hip arthroplasty after treatment of displaced femoral neck fractures (€26,399 per patient until 2 years) were rehabilitation and nursing homes. Most of the costs were made in the first year. Reducing costs after hip fracture surgery should focus on improving the duration and efficiency of the rehabilitation phase.