Chronic opioid use (COU) after traumatic injuries is a global health concern. COU after trauma delays recovery and increases the risk of long-term drug dependence. However, the population-prevalence and factors associated with COU after traumatic injury in South Korea remain unclear. We aimed to estimate the prevalence of COU and associated risk factors in patients after trauma in South Korea. A historical cohort study using the population-representative database including 1,103,405 South Korean subjects, patients admitted due to a newly diagnosed trauma (n = 65,444) or nontraumatic etiologies (n = 338,321) from January 1, 2003, to June 30, 2015, were analyzed. COU was defined as the prescription of opioid in the first 3 to 6 months from the index date. Prevalence of COU was summarized. A multivariable logistic regression analysis was conducted to investigate association of COU with traumatic injuries, accounting for a priori sociodemographic and clinical risk factors. A total of 13.5% and 12.6% of patients were found to be chronic opioid users in the trauma and the control group, respectively. The adjusted odds ratio (aOR) (95% CI) of COU in the injured compared to the noninjured was 1.13 (1.01 to 1.16), when controlling for age group, sex, calendar year, area of residence, previous opioid use, comorbidity, surgery during the index admission and intensive care unit care. Risk factors included being aged 65 to 74 years (aOR = 2.87; 95% CI = 2.73 to 3.01), aged ≥ 75 years (aOR = 2.48; 95% CI = 2.35 to 2.62), and history of previous opioid use (aOR = 3.27; 95% CI = 3.21 to 3.34) were the most significant risk factors of COU, independent of injury. COU was prevalent both in the injured and noninjured patients, with slightly increased risk of COU in those sustaining traumatic injury compared to those who were noninjured. Further stud y to address prevalent COU in South Korea is required to avoid opioid-related harms.