This paper examines the validity of the Structured Clinic Interview for DSM-IV (SCID) I and II in a sample of Veterans seeking treatment for substance use disorders (SUDs). Participants (N = 183) initially receiving residential or outpatient treatment for SUDs completed the SCID I and II. More than one-third of participants met criteria for an Axis I disorder, and almost one-half met criteria for an Axis II disorder. Concurrent, discriminant, and predictive validity were examined for diagnoses of SUDs and antisocial personality disorder (APD), as well as symptoms of depression, anxiety, and thought disorder. Results generally provided strong support for the concurrent, discriminant, and predictive validity of the SCID I diagnoses of alcohol use disorders (AUDs) and strong support for the concurrent and discriminant validity of drug use disorders (DUDs). There was mixed support for the concurrent validity of APD. Predictive validity for DUDs or APD was not supported.