This thesis explored the ability of the Minnesota Multi-phasic Personality Inventory to predict the during-treatment behavior of drug addicts. The MMPI's of eighty-five male patients of the Indianapolis Veterans Administration Drug Treatment Unit were compared to counselorr ratings of each addict's behavior while on inpatient status. It was found that the MMPI was significantly related (p <.01) to the counselor ratings. The strongest predictor was the MacAndrew Alcoholism Scale which had a mean raw score of 28.55. The utility of the resulting regression formula for giving information about future behavior of the individual drug abuser was also discussed.