Youths experiencing unstable housing face higher risks for poor physical, mental, and sexual health outcomes and increased risk for suicide compared with their peers experiencing stable housing. In addition, youths of color and sexual minority youths are disproportionately more likely to experience homelessness. For the first time, in 2021, the nationally representative Youth Risk Behavior Survey included an item assessing housing stability, or nighttime residence among students in grades 9–12 in the United States. During 2021, 2.7% of U.S. high school students experienced unstable housing. Among racial and ethnic subgroups, Native Hawaiian or other Pacific Islander youths were most likely to experience unstable housing, followed by American Indian or Alaska Native and Black youths. Sexual minority (lesbian, gay, bisexual, and questioning or other) youths were more likely to experience unstable housing compared with their heterosexual peers. Compared with students who were stably housed, students who were unstably housed were more likely to engage in risky sexual behaviors, substance use, and suicide ideation and attempts, and to experience violence. These findings highlight which adverse health risks and behaviors are elevated among youths experiencing housing insecurity. Focused public health interventions are required to address the disproportionate burden of health risks prevalent among youths who are unstably housed.