ABSTRACTThis study reports on three years of prospective, longitudinal data on the psychological well-being of the human handlers and the health and behavior of the search and rescue dogs deployed in New York City and Washington, DC in the aftermath of the terrorist attacks on September 11, 2001. Eighty-five human handlers (63 deployed and 22 controls) and ninetyfour dogs (66 deployed, 28 controls) were assessed at multiple time points including 6 months, 1 year, 2 years, and 3 years after the 9/11 attacks. Humans were assessed for psychological health by structured clinical interview and self-report. Dogs were assessed for physical health and behavior by veterinary records and handler report. For humans, deployment after 9/11 did indeed represent a relatively short-term risk factor for developing symptoms of depression and posttraumatic stress disorder (PTSD). By and large, however, the sample showed remarkable resilience as a whole, and overall rates of DSM-IV diagnoses were quite low. By year 3, 9/11 deployment no longer conferred any special risk. On the other hand, long-term employment in an emergency profession did emerge as a significant risk factor for symptoms of PTSD by year 3. With respect to the interaction between handler emotional well-being and canine health and behavior, we found that physical illness and/or death in the dog was prospectively associated with greater symptoms of depression in the handler. We also found that symptoms of depression and PTSD in the handlers prospectively predicted behavioral problems in the dogs over time. Separation anxiety, attachment/attention seeking, chasing, and excitability emerged in the dogs at 1 year. Behavioral problems escalated to aggression towards other dogs at year 2 and separation anxiety, aggression towards other dogs, and aggression towards strangers at year 3. Like any relationship, the partnership between a handler and his or her working dog can confer both protection—when the relationship is going well and both members are healthy—and vulnerability—when either member is physically ill or psychologically or behaviorally distressed.