Experiencing severe flooding tends to negatively impact mental health, creating a significant public health issue. Moreover, extreme events can co-occur, magnifying potential impacts. Understanding the combined mental health impacts of floods and COVID-19 is a research gap we addressed by conducting 400 face-to-face surveys in October 2023 in Hue City, Vietnam, where residents faced simultaneous flooding and COVID-19 in 2020.</p> <p>The respondents' mental health was assessed using the Kessler psychological distress scale (K6), revealing that 20 % of the respondents experienced mental health distress, while 80 % did not report such distress. Binary logistic regression models demonstrated that among twelve flood stressors, facing ‘livelihood difficulties’, ‘seeing dead human bodies’, and ‘being rescued’ relate significantly to mental distress. Meanwhile, ‘impacts on individual health’ and ‘interrupted education’ are the two significant COVID-19 stressors. These five factors stay significant when combined. Additionally, a multivariable regression model revealed the combined effects of flood and COVID-19 when comparing the ORs of four groups ranging from ‘No flood stress & No Covid stress’ to ‘Flood stress & Covid stress’. The effect size is largest for those who experienced flood and COVID-19 impacts, followed by those who suffered only floods and those who faced only COVID-19, with the smallest effect size.</p> <p>These findings underline the need to address public health problems caused by multiple risks, which is still a significant gap in developing countries. Furthermore, psychological impacts could be reduced by providing additional support to at-risk communities, like managing human remains, rehearsing evacuation plans, preventing school closures, and setting up public health infrastructure for psychological assistance.