Objectives: Hurricane Katrina was an intense tropical cyclone that made landfall in the United States (US) in August 2005, causing catastrophic damage in several states. This study examined the impact of Hurricane Katrina on mental health status among US adults. Methods: Multilevel regressions based on the difference-in-differences study design were performed on individual-level data (N = 70,267) retrieved from the Behavioral Risk Factor Surveillance System 2004-2006 surveys. Results: Hurricane Katrina was found to be associated with an increase of 0.68 poor mental health days among residents of Katrina-affected states. The negative impact of Hurricane Katrina on mental health status tended to be larger among Louisiana residents, women, young and middle-aged adults, lower income respondents, and those with poor/fair self-rated physical health than among Mississippi residents, men, older adults, higher income respondents, and those with good/excellent self-rated physical health. Conclusion: Hurricane Katrina adversely impacted mental health of residents in Katrina-affected states, and the impact differed across population subgroups. Future studies should investigate other potential risk and protective factors for the mental health consequences of disasters. They should examine long-term impacts on mental health following disasters to better inform population-based mental health interventions for disaster survivors.