This paper aims to test the clinical and research utility of a Spanish version of the Teen-Addiction Severity Index (T-ASI) in adolescents with psychiatric disorders attending a treatment programme. Eighty adolescents, 12 to 17 years old (Mean=14.5; SD=1.48) were evaluated with a research battery including the T-ASI to obtain data on socio-demographics, psychopathology, drug use, family environment and school achievement. The Substance Use scale of the T-ASI correlated significantly (Rho=0.90, p</=0.01) with an ordinal measure of "pattern of any drug use", and with "subjective problems with drugs" (rank 0-32) (Rho=0.69, p</=0.01). All T-ASI scales, except Psychiatric Status, showed significant correlations with externalized scores of the Children's Behavior Checklist (CBC) and also discriminated between patients with and without Substance Use Disorders. To conclude, Spanish version of the T-ASI shows adequate psychometric properties to be used as a clinical and research instrument in Spanish-speaking adolescents with psychiatric disorders.