Community and population-based studies show that non-heterosexual youth (i.e., sexual minority youth) are at significantly higher risk for an array of poor health and mental health outcomes in comparison to their heterosexual peers. These outcomes include acquiring sexually transmitted infections, becoming pregnant or fathering a pregnancy, anxiety, depression, suicidality, and suicide. In addition, sexual minority youth experience higher rates of verbal, physical and/or sexual victimization and are at greater risk for substance abuse and unsafe sexual activity (e.g., inconsistent use of condoms and multiple sexual partners), which may further increase the risk for poor health and mental health outcomes. This three-study dissertation presents findings from the National Longitudinal Study of Adolescent Health (Add Health), a nationally representative school-based study. Data were taken from Wave I of Add Health, and consisted of a weighted sample of 18,924 youth in grades 7 - 12 with a subsample of 1,388 sexual minority youth. Study 1 used chi-square analyses to test group differences in unmet health and mental health need, foregone healthcare and barriers to healthcare, and service use setting by sexual minority status. Study 2 used logistic regression to test individual and family characteristics that predict unmet health and unmet mental health need among youth. Study 3 used multilevel logistic regression to test the impact of school-based mental health services and school location (over and above individual and family characteristics) on mental health service use. Results showed significantly higher rates of unmet health and mental health need among sexual minority youth, who reported more foregone healthcare and cited healthcare barriers related to confidentiality concerns. Sexual minority youth obtained mental healthcare most often at private doctor's offices and less often at school. Higher levels of parent connectedness significantly reduced the odds for an unmet health or mental health need among youth, regardless of sexual minority status. Similarly, regardless of sexual minority status, school-based mental health services significantly increased odds that youth with mental health need would obtain mental health services. Findings highlight the need to develop tailored interventions aimed at youth, parents, schools, and healthcare providers to promote access to services among sexual minority youth. Advisors/Committee Members: Williams, Kelly A., Chapman, Mimi.