This study examines the factors related to referrals of adolescents with substance use disorders to substance abuse or mental health treatment by their medical providers. Administrative and chart review data from the membership of a large private health maintenance organization (HMO) were collected from a probability sample of 400 adolescents, ages 13-18, who were diagnosed with a substance use disorder in 1999. Logistic regression analyses examined referral to substance abuse treatment and referral to mental health treatment in the aggregate and stratified by gender. Documented use of both alcohol and another illicit drug, and legal problems increased likelihood of referral to substance abuse and mental health treatment, whereas diagnoses of alcohol and marijuana use disorders decreased likelihood of referral to substance abuse treatment. Mental health diagnoses played a limited role in both types of referrals, although specific psychosocial problems were associated with increased likelihood of referrals. Treatment history and location of first mention of problem were significant predictors of referral. There were no gender differences in referral rates to either substance abuse or mental health treatment; however predictors of referral differed by gender. These findings extend our knowledge about factors that influence clinicians' treatment referrals of adolescents with substance abuse diagnoses and have implications for influencing clinician referral behavior within health plans.