To monitor priority health-risk behaviors among youth and young adults, the Centers for Disease Control and Prevention (CDC) developed the Youth Risk Behavior Surveillance System (YRBSS). The YRBSS includes national, state, territorial, and local school-based surveys of high school students in grades 9-12. In addition, some states, territories, and cities conduct a school-based Youth Risk Behavior Survey (YRBS) among middle school students. In 2005, four U.S. territories (Commonwealth of the Northern Mariana Islands [CNMI], Palau, Guam, and Commonwealth of Puerto Rico) conducted a YRBS among students in grades 9-12, and three territories (CNMI, Palau, and Guam) conducted a YRBS among students in grades 6-8. This report summarizes data from three territories with weighted high school data (CNMI, Palau, and Puerto Rico) and from two territories with weighted middle school data (CNMI and Palau). Surveys that had a census or a scientifically selected sample of students, appropriate documentation, and an overall response rate of 60% or more were weighted. Although Guam conducted both a middle school and a high school YRBS, it did not obtain weighted data. Therefore, the unweighted data from Guam are omitted from this report. All the surveys were conducted during spring 2005. Puerto Rico, CNMI, and Republic of Palau are all U.S. territories. For the purpose of this report, they are divided into two groups: Pacific Island territories and Puerto Rico. CNMI and Palau share similar culture and demographics, while Puerto Rico has more commonalities with the United States than it does with the Pacific Island territories. Thus, in the discussion section, CNMI and Palau data are compared, while Puerto Rico and the United States are compared. Adults and adolescents in the Pacific Islands encounter a double burden of disease, facing both communicable diseases such as tuberculosis and malaria and chronic diseases such as cardiovascular diseases and diabetes. Puerto Ricans are more at risk for chronic diseases than communicable diseases. Although human immunodeficiency virus (HIV) infection is one of the leading causes of mortality for Puerto Rican adults aged 40-44 years, cardiovascular diseases (representing 29% of all deaths) are the leading cause of death for this population. The health issues that contribute to the burden faced by CMNI, Palau, and Puerto Rico are causally related to the modifiable risk behaviors measured by the YRBSS: unintentional injuries and violence; tobacco use; alcohol and other drug use; sexual behaviors that contribute to unintended pregnancy and sexually transmitted diseases (STDs), including HIV infection; unhealthy dietary behaviors; and physical inactivity. The data in this report provide a glimpse, not only at the current burden faced by the youth of CNMI, Palau, and Puerto Rico, but also at the burden they will face as adults. (Contains 1 figure and 141 tables.)