The study examined the 30-day and lifetime prevalence of DSM-IV alcohol and drug disorders among state prison inmates. A sample of 400 inmates consecutively admitted to a state prison reception center were assessed for alcohol and drug disorders using the Structured Clinical Interview for DSM-IV (SCID-IV). Test-retest reliabilities were calculated for the SCID-IV. Lifetime substance abuse or dependence disorders were detected among 74% of inmates, including over half who were dependent on alcohol or drugs. For the 30 days prior to incarceration, over half of the sample were diagnosed as having substance abuse or dependence disorders, including 46% who were dependent on alcohol or drugs. Black inmates were significantly less likely to be diagnosed as alcohol dependent than whites or Hispanics. The high rates of substance use disorders are consistent with previous findings from other studies conducted in correctional settings and reflect the need to expand treatment capacity in prisons.