Study Objectives: Our objective was to investigate the relationship between military occupation and diagnosed insomnia following combat deployment. Methods: This retrospective cohort study was conducted using existing electronic military databases. Eligible participants were military personnel with a deployment to Iraq, Afghanistan, or Kuwait between 2005 and 2009. A total of 66,869 U.S. Navy and U.S. Marine Corps service members constituted the study sample and were categorized by military occupation. Military medical databases were used to abstract information on insomnia diagnoses and prescription medications. Results: The overall prevalence of diagnosed insomnia was 3.4%. In multivariable logistic regression, personnel in law enforcement (odds ratio = 1.62; 95% confidence interval, 1.28-2.04), motor transport (odds ratio = 1.38; 95% confidence interval, 1.14-1.66), and health care occupations (odds ratio = 2.24; 95% confidence interval, 1.85-2.71) had significantly higher odds of an insomnia diagnosis following deployment than did those in infantry occupations. These results remained unchanged after excluding those who reported posttraumatic stress disorder symptoms. Nonbenzodiazepine sedative/hypnotics were prescribed for 44.2% of those with insomnia, and prescription patterns differed by occupation. Conclusions: These results suggest thatmilitary occupation may play a primary role in the onset and management of insomnia. The findings provide a rationale for targeting individuals in insomnia-susceptible occupations with better methods to prevent and/or minimize sleep issues during and after combat deployment.