Importance: Time to surgical intervention is an oft-investigated potentially modifiable risk factor for complications after mandible fracture. Objective: To identify novel risk factors for malunion/nonunion after mandible fracture and determine the impact of treatment delay on malunion and nonunion after open reduction of mandible fractures. Design: Retrospective cohort. Setting and Participants: Encounter billing records from the New York State Inpatient Databases, State Emergency Department Databases, and State Ambulatory Surgery Databases. Patients aged 18 years and older with isolated mandible fracture in the emergency department or inpatient setting from January 1, 2006 to September 30, 2015. Main Outcomes and Measures: Mandibular Malunion/Nonunion. Results: A total of 19,152 adults were diagnosed with isolated mandible fracture. After fracture, 247 patients (1.3%) developed mandibular malunion or nonunion. In multivariable analysis, patients with open fractures (odds ratio [OR] 1.93, confidence interval [95% CI] 1.40-2.65), body fractures (OR 2.00, 1.50-2.65), alcohol abuse (OR 1.61, 1.22-2.11), diabetes mellitus (OR 1.57, 1.02-2.42), and Medicaid insurance (OR 1.46, 1.03-2.07) had increased risk, whereas patients with subcondylar fractures had reduced risk (OR 0.45, 0.28-0.72) of mandibular malunion/nonunion. The risk of mandibular malunion/nonunion after open reduction increased with treatment delay until 6-7 days after presentation (OR 1.84, 1.11-3.06). Conclusion and Relevance: Although treatment delay is often unavoidable, these findings suggest that physicians should consider early intervention in patients requiring open reduction of mandible fractures when able.