BACKGROUND Youth in detention represent a medically underserved population at risk for a variety of medical and emotional disorders. OBJECTIVE To determine prevalence of STDs and high-risk sexual behaviors for HIV/STD among adolescent males admitted to a juvenile detention facility. METHODS Cross-sectional study of behavioral risk factors and STD prevalence among detained males, 11 to 18 years of age. Study subjects were interviewed for behavioral history and screened for STD. RESULTS The median number of lifetime partners of the population was 8 (range 1-100), the number of partners in the preceding 4 months was 2 in median (range 0-30), 59% used a condom with their last sex, and consistent condom use in the past 4 months was reported by 37%. A history of sexual intercourse within the last one week was reported by 43%. Chlamydia trachomatis infection rate was 6.9% (66/957), Neisseria gonorrhoeae 4.5% (42/940) and syphilis 0.9% (8/930) including one who seroconverted while in detention. Overall, 12% (109/908) of subjects tested for all three infections were positive for at least one STD. Stepwise logistic regression analysis showed that greater than one partner in the previous 4 months (OR 1.53, 95% confidence interval [95% CI] 1.18-1.98), inconsistent or no condom use in the preceding 4 months (OR 1.77, 95%CI 1.37-2.28), a history of recent STD (OR 1.80, 95%CI 1.33-2.42) and greater than five lifetime partners (OR 2.03, 95% CI 1.41-2.92) were independent predictors of these STDs in this population. CONCLUSIONS Detained juvenile males in our study were at a high-risk for STD/HIV infections and probably form a core group of STD transmitters. Vigorous attempt to reduce STD reservoir and change behavior of juveniles in detention, such as our study subjects, is urgently needed for the control of the STD/HIV infections.