Background <p>Intent-based injury surveillance requires distinction between injury intent and mechanism, particularly when datasets include anatomical trauma and non-traumatic external-cause injuries such as drug intoxication. This study compared mechanisms, incidence, regional variation, transfer pathways, and short-term outcomes between intentional and unintentional severe external-cause injuries in South Korea.</p> Methods <p>This retrospective nationwide study used the Korea Disease Control and Prevention Agency Community-Based Severe Trauma Survey (2016–2020). The source population comprised patients with severe trauma, non-traumatic severe injury, or mass casualty incidents transported to emergency departments by 119 Emergency Medical Services and confirmed through hospital record review. Intentional injury was defined as self-harm/suicide or violence/homicide, and unintentional injury as recorded unintentional injury. Drug intoxication was treated as a mechanism, not as intent. Descriptive analyses used the full cohort, whereas primary multivariable models used the prespecified non-intoxication cohort. Age-specific incidence and mortality were calculated as pooled 2016–2020 rates using summed annual population denominators. Logistic regression estimated adjusted odds ratios (aORs) for emergency department (ED) and post-admission survival.</p> Results <p>Among 230,302 transported cases, 55,513 were intentional and 174,789 were unintentional; 45,093 involved drug intoxication. Intentional injuries were more commonly associated with drug intoxication and hanging or strangulation, whereas unintentional injuries were mainly transportation- or fall-related. Out-of-hospital cardiac arrest was more frequent after intentional injuries (21.8% vs. 9.8%), as were ED death (19.6% vs. 9.8%) and documented ED or in-hospital mortality after ED presentation (23.3% vs. 13.7%). In the non-intoxication cohort, intentional injury was associated with lower ED survival (aOR, 0.215; 95% CI, 0.207–0.222) and lower post-admission survival (aOR, 0.561; 95% CI, 0.521–0.604). Age-specific incidence and mortality were generally higher for unintentional injuries, whereas transported-case fatality was higher for intentional injuries.</p> Conclusions <p>Intentional and unintentional external-cause injuries differed in mechanism distribution, prehospital deterioration, age-specific burden, transfer pathways, and outcomes. Drug intoxication should be distinguished from injury intent and anatomical trauma. These findings support clear intent-mechanism classification and targeted prevention and emergency care strategies.</p>