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BACKGROUND: Although most nondisplaced or minimally displaced femoral neck fractures are routinely treated with internal fixation, high rates of secondary surgical procedures are common, especially in the elderly population. Primary arthroplasty in elderly patients has been proposed as an alternative treatment to reduce the need for a secondary surgical procedure. The objective of this study was to describe the rate of conversion to arthroplasty within 5 years after internal fixation of nondisplaced femoral neck fractures in patients ≥60 years of age. METHODS: In this observational cohort study of prospectively collected data from the Swedish Fracture Register (SFR) between 2012 and 2018, cross-matched with the Swedish Arthroplasty Register (SAR), 5,428 nondisplaced femoral neck fractures in patients ≥60 years of age were included. Competing risk analysis was used to estimate conversion rates to arthroplasty and mortality in various age groups at 1, 2, and 5 years. RESULTS: The cumulative incidence function (CIF) for conversion to arthroplasty was 6.3% at 1 year, 8.1% at 2 years, and 10.1% at 5 years. The conversion rates within 2 years were 6.5% in 60 to 69-year-olds, 9.6% in 70 to 79-year-olds, and 7.8% in ≥80-year-olds. Women had a higher risk of conversion; the hazard ratio (HR) was 1.49 (95% confidence interval [CI], 1.19 to 1.87). The cumulative mortality was 21.3% (95% CI, 20.3% to 22.5%) at 1 year, 31.3% (95% CI, 30.0% to 32.6%) at 2 years, and 54.9% (95% CI, 53.1% to 56.7%) at 5 years. Mortality was higher in men at all time points, and the adjusted 1-year HR was 1.79 (95% CI, 1.61 to 2.00). CONCLUSIONS: One in 10 patients ≥60 years of age treated with internal fixation for a nondisplaced femoral neck fracture underwent conversion to arthroplasty within 5 years, and more than one-half of the conversions occurred within the first year. The risk of conversion was highest in women and in patients 70 to 79 years of age. These data warrant further studies in this frail patient group to identify subgroups of patients who would benefit from primary arthroplasty for nondisplaced femoral neck fractures. LEVEL OF EVIDENCE: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.