OBJECTIVE: This study examined national patterns of outpatient service use by veterans from regions affected by Hurricane Katrina. METHODS: Analyses tracked use of general medical and mental/substance use services in September and October through December 2005 in New Orleans and Biloxi-Gulfport compared to a cohort receiving care during the same months in the previous 2 years. RESULTS: In adjusted models, veterans from New Orleans and Biloxi-Gulfport were, respectively, 73% and 41% less likely in September 2005 to use any outpatient services as were cohorts from 2003-2004. Particularly in New Orleans, the relative decline in service use was substantially greater for specialty mental health and substance use services than for general medical services. CONCLUSIONS: Although many veterans were able to obtain care after Hurricane Katrina, there was a substantial disruption in delivery of Veterans Administration services, with disproportionate declines in mental health and substance use care.