There has been relatively little research on the degree to which measures of lifetime history of substance abuse add to the prediction of risk based on actuarial measures alone among sexual offenders. This issue is of relevance in that a history of substance abuse is related to relapse to substance using behavior. Furthermore, substance use has been found to be related to recidivism among sexual offenders. To investigate whether lifetime history of substance abuse adds to prediction over and above actuarial instruments alone, several measures of substance abuse were administered in conjunction with the Sex Offender Risk Appraisal Guide (SORAG). The SORAG was found to be the most accurate actuarial instrument for the prediction of serious recidivism (i.e., sexual or violent) among the sample included in the present investigation. Complete information, including follow-up data, were available for 250 offenders who attended the Regional Treatment Centre Sex Offender Treatment Program (RTCSOTP). The Michigan Alcohol Screening Test (MAST) and the Drug Abuse Screening Test (DAST) were used to assess lifetime history of substance abuse. The results of logistic regression procedures indicated that both the SORAG and the MAST independently added to the prediction of serious recidivism. The DAST did not add to prediction over the use of the SORAG alone. Implications for both the assessment and treatment of sexual offenders are discussed. (Contains 3 tables.)