The research concerning intellectual functioning in addict populations has not addressed basic questions concerning why and how intelligence quotients (IQ) might be related to drug addiction. A study was undertaken to estimate intellectual functioning based upon a demographic profile for Wechsler Adult Intelligence Scale-Revised (WAIS-R) Full Scale IQ in order to determine its relationship with variables representing initiation, continuation, relapse, and cessation of daily opioid use. Estimated IQs were used to describe a large former opioid addict sample (N=486) from the 12-year follow-up study of the Drug Abuse Reporting Program (DARP). Results were compared with those from previous studies of various drug users and non-users, and a correlational analysis was performed. The results indicated that the average estimated IQs for the DARP sample were comparable to mean IQs for both the WAIS-R standardization sample (N=1,880) and previous studies. IQ was significantly related to length of addiction career; the higher the IQ, the shorter the career. Other more complex relationships were found for variables used to represent intraindividual factors such as satisfaction with self or family, interpersonal factors such as family or peer influence, and other variables of interest. (NRB)