Objectives: For patients with femoral neck fractures, total hip arthroplasty ( THA) demonstrates superior outcomes compared with hemiarthroplasty. However, hemiarthroplasty remains a common treatment for femoral neck fractures and the conversion rates are unknown. We compared the results of the 2 procedures using a Medicare database. Methods: We assembled a cohort of 70,242 patients 65 to 90 years of age with an ICD9 diagnosis and matching Current Procedure Terminology code for femoral neck fracture between 2008 and 2012. Patients were followed forward for 2 years minimum. Incidences of dislocation and mortality were measured. Reoperation for revision of THA or conversion of hemiarthroplasty to THA was assessed by Current Procedure Terminology code. Groups were compared through proportional hazard models controlling for age, race, sex, and comorbidity index. Results: Hemiarthroplasty represented 95% of the patients treated using arthroplasty for femoral neck fracture. The proportional hazard of reoperation and dislocation were significantly lower for hemiarthroplasty than THA (P < 0.0001 for both). At 2 years, fewer than 2% of hemiarthroplasty patients underwent conversion to total hip replacement. Patients treated with THA were more likely to be alive for 2 years (adjusted hazard ratio = 1.67, 95% confidence interval: 1.59-1.92). Conclusion: Patients treated with hemiarthroplasty after femoral neck fractures had significantly lower proportional hazard of reoperation than those treated with THA. THA may be associated with lower mortality.