Reserve and National Guard forces have been mobilized to an unprecedented degree in recent overseas conflicts. There is concern that rates of psychological problems may continue to rise for many years after deployment. The authors conducted a cohort study of 552 United Kingdom Reservists who deployed to Iraq in 2003 and 391 nondeployed Reservists. Measures of mental health and social functioning were collected a mean of 16 months and 4.8 years after return from possible deployment. At the first follow-up, deployment was associated with increased common mental disorder, post-traumatic stress disorder (PTSD), and poor general health. By the second follow-up, those who had deployed were no longer at increased risk for common mental disorder or poor general health and had good levels of social functioning. However, those who deployed continued to have over twice the odds of PTSD (odds ratio = 2.42, 95% confidence interval: 1.04, 5.62) and were more likely to report actual or serious consideration of separation from their partner. In conclusion, the authors found that the majority of mental health and social problems following deployment are transient. However, Reservists who deployed in the Iraq War remain at increased risk of PTSD and relationship problems 5 years after their tour of duty.