BackgroundSexually transmitted infections (STIs) are prevalent in the U.S. military. However, there are limited data on risk-factor differences between sexes.MethodsWe used data from the 2008 Department of Defense Survey of Health Related Behaviors among active duty military personnel to identify risk factors for self-reported STIs within the past 12 months and multiple sexual partners among sexually active unmarried service members.ResultsThere were 10,250 active duty personnel, mostly white (59.3%) aged 21 to 25 years (42.6%). The prevalence of any reported STI in the past 12 months was 4.2% for men and 6.9% for women. One-fourth of men and 9.3% of women reported 5 or more sexual partners in the past 12 months. Binge drinking, illicit sub...