Background There are relationships among morbidity, experiences before, during, and after participation in overseas military operations. Methods U.S. servicemembers who deployed to Bosnia-Herzegovina during a 4-year period were classified based on their last hospitalizations prior to deploying. Hospitalization rates during and following deployment were calculated in relation to the timing and causes of pre-deployment hospitalizations. Results Deployers ever hospitalized pre-deployment were 120% and 50% more likely to be hospitalized during and following deployment, respectively. For nearly every category of diagnoses, hospitalization rates during and following deployment were highest among those hospitalized for the same category, intermediate among those hospitalized for other categories, and lowest among those not hospitalized prior to deploying. Deployers hospitalized within I month, 2-3 months, or > 3 months of deploying were 3.8, 2.6, and 1.4-times more likely, to be hospitalized during deployment. Conclusions The nature and recency of prior hospitalizations significantly determine during and post-deployment hospitalization risks. Published 2002 Wiley-Liss, Inc.(dagger)