Young adults experience the highest rates of sexually transmitted diseases (STDs) in the United States and gender and racial/ethnic differentials in STD prevalence persist. Rich data are available to investigate an array of sociodemographic and behavioral risk factors that might explain variation in STD infection. These data also include biomarker test results enabling an investigation of current infection among a population-based sample of youth. We use data from Wave III of the National Longitudinal Study of Adolescent Health (Add Health) to examine sociodemographic and behavioral risk correlates of STDs, using nested binary logistic regression techniques. We consider whether respondents who refused or were unable to provide urine samples differ from those who provided urine samples. We also consider whether respondents whose specimens were not used, or whose specimens were used but for whom no definitive test result was obtained, differ from individuals for whom definitive test results were obtained. Finally, we explore sociodemographic and behavioral correlates of positive test results for those for whom definitive test results were obtained. All analyses are weighted and account for the complex study design of Add Health. Current STD infection is associated with a number of sociodemographic characteristics, including age, gender, and race/ethnicity, the effects of which differ depending on the specific pathogen. The effects of the sociodemographic characteristics remain even after accounting for differences in sexual risk behaviors. Future research should explore the contribution of partner characteristics and behaviors as well as sexual networks in explaining variation in STD infection.