OBJECTIVES: To determine risk factors for early conversion THA after operative treatment of acetabular fractures. DESIGN: Retrospective cohort. SETTING: Level I trauma center. PATIENTS AND INTERVENTION: We reviewed 685 operative acetabular fractures at our institution from 2011-2017, with median follow-up of 12 months (4-105 months). MAIN OUTCOME MEASUREMENT: Multivariable regression analysis was performed after univariate analysis to identify independent risk factors for conversion THA. Sensitivity analysis was performed with minimum follow-up set at 6-months and 12-months. RESULTS: One-hundred eight patients (16%) underwent conversion THA, with 52% of conversions occurring within 1 year, an additional 27% within 2 years, and the remaining 21% within 6 years of the index acetabular ORIF. The median time to conversion THA was 11.5 months (0.5-72 months). The risk of conversion THA by fracture pattern was: 53/196 (27%) transverse posterior wall, 12/52 (23%) T-shaped, 10/68 (15%) posterior column with posterior wall, and 25/207 (12%) posterior wall. Independent risk factors for early conversion included: transverse posterior wall fracture, protrusio, hip dislocation, increased BMI, increased age, infection and dislocation after ORIF. Independent risk factors for early conversion THA specific to patients with transverse posterior wall fractures include only increased age and BMI. Sensitivity analysis showed no change in results using either 6-month or 12-month minimum follow-up. CONCLUSION: Transverse posterior wall fractures have a high risk of early conversion THA compared to other acetabular fracture patterns, especially when in combination with other significant risk factors. Consideration for different and novel management options warrants further study in this subset of acetabular fracture patients. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.