The reviewed research findings pertaining to the effects of drugs on criminality encompass drugs and violent crime, crime changes associated with drug-use changes, crime levels during drug abuse periods, the costs of street-level addiction and crime, economic returns per crime, patterns of drug use and crime, and costs for victims and society. A primary overall research finding is that heroin abusers, especially daily users, commit an extraordinary amount of crime, motivated by their need to obtain the drug. Most of the heroin abusers researched had little legally generated income. Findings also indicate that the amounts and types of crimes committed by drug abusers vary considerably. For the majority of users, current criminality patterns are strongly influenced by current drug usage. A policy implication is that drug treatment and education programs should focus on the most frequent drug users so as to have maximum impact on drug-related crime. Graphic data indicate changes in criminality by addiction status and the crime rates of street heroin abusers by drug usage level. Fifteen references are listed.