Objectives: This study aimed to determine the prevalence of severe dengue and examine the associations between pre-existing comorbidities and disease severity. Methods: This retrospective study examined patients with dengue fever who received inpatient treatment at a hospital in northern Vietnam between January 1, 2022, and December 30, 2024.Patients were categorized into 2 groups—severe dengue and non-severe dengue—based on the 2009 World Health Organization criteria. Multivariable logistic regression was performed to assess factors associated with severe dengue. Results: Among 3,692 patients, the prevalence of severe dengue was 1.5%. Patients with any pre-existing comorbidity had higher odds of severe dengue compared to those withoutcomorbidities (adjusted odds ratio [aOR], 2.06; 95% confidence interval [CI], 1.20–3.53). Having2 or more comorbidities was also associated with higher odds of severe dengue (aOR, 2.26; 95%CI, 1.18–4.33). Among individual conditions, hyperlipidemia was associated with severe dengue (aOR, 2.32; 95% CI, 1.17–4.81). Certain combinations of comorbidities, including hypertension with hyperlipidemia (aOR, 2.88; 95% CI, 1.39–5.97), hypertension with cardiac disease (aOR, 4.39; 95% CI, 1.30–14.79), and hyperlipidemia with cardiac disease (aOR, 4.02; 95% CI, 1.19–13.53),were also associated with higher odds of severe dengue. Conclusion Pre-existing comorbidities, particularly cardiometabolic conditions, wereassociated with higher odds of severe dengue. Considering comorbidity profiles at hospitaladmission may help identify patients who require closer clinical monitoring.