QUESTIONS/PURPOSES: The aim of this study was to identify prognostic factors associated with a poor quality of reduction and their relationships. METHODS: Data from medical charts for all patients admitted with acetabular fractures operated by open reduction and internal fixation (ORIF) from 2005 to 2014 were extracted. A total of 156 patients with a mean age of 40.3 years were included. All patients were reviewed at six months of follow-up. The prognostic factors analyzed were clinical and radiological factors. A new radiological parameter was also studied: the scanographic roof-arc angle. Specific statistical analysis was performed using a logistic regression model. RESULTS: Using a multivariate analysis logistic regression model: roof impaction (p = 0.001; OR = 6.59; CI 95% [2.01-20.97]), transverse + posterior wall (p = 0.03, OR = 2.52; CI 95% [1.46-13.65]) and surgeons in training (p = 0.02; OR = 1.24; CI 95% [1.07-3.32]) were three independent prognostic factors. Lower values of medial and posterior scanographic roof-arc angle were associated with unsatisfactory reduction. A significant association between unsatisfactory reduction and posterior roof arc angle < 61° was found. CONCLUSIONS: Three independent prognostic factors associated with a risk of unsatisfactory reduction in ORIF for acetabular fractures were identified: roof impaction, transverse + posterior wall fracture and surgeons in training. Scanographic roof-arc angle seems to be a new prognostic factor. Level of Evidence Level 4 retrospective study.