The objective of this study was to evaluate the distributions of U.S. Marine Corps and Army wounded in action (WIA) and disease and nonbattle injury (DNBI) casualties during Operation Iraqi Freedom Major Combat Phase (OIF-1) and Support and Stability Phase (OIF-2). A retrospective review of hospitalization data was conducted. chi2 tests were used to assess the Primary International Classification of Diseases, 9th Revision (ICD-9), diagnostic category distributions by phase of operation, casualty type, and gender. Of the 13,071 casualties identified for analysis, 3,263 were WIA and 9,808 were DNBI. Overall, the proportion of WIA was higher during OIF-1 (36.6%) than OIF-2 (23.6%). Marines had a higher proportion of WIA and nonbattle injuries than soldiers. Although overall DNBI distributions for men and women were statistically different, their distributions of types of nonbattle injuries were similar. Identifying differences in injury and illness distributions by characteristics of the casualty population is necessary for military medical readiness planning.