This study examined the convergent validity of the Timeline Followback (TLFB) for individuals with comorbid (Axis I and/or Axis II) psychiatric disorders in a sample of persons (N=150) engaged in residential treatment for substance use disorders (SUDs). Approximately one-half of the sample was diagnosed with at least one comorbid psychiatric disorder. Validity was assessed comparing data from the TLFB with data from the Addiction Severity Index (ASI) and collateral reports. For the entire sample, data from the TLFB was significantly correlated with data from the ASI and collateral reports of substance use. No significant differences were found between those with and those without a comorbid psychiatric disorder, suggesting that the TLFB was equally valid for both groups.