The three issues studied were the temporal sequence of events regarding the onset of heroin addiction and the beginning of criminal behavior, the types and frequencies of crimes committed by heroin addicts, and the impacts on criminality of an addict's subsequent periods of abstinence or addiction. Discussion of these issues was based on a critical review of pertinent scientific reports and on interview data obtained from 243 male opiate addicts in Baltimore. The subjects were a random sample chosen from a list of 4,069 known opiate users arrested or identified by the Baltimore Police Department between 1952 and 1971. The 3-hour interviews focused on drug use, criminal behavior, work, living arrangements, drug selling, and sources of income. The numbers of crime-days per year at risk were found to show a sixfold increase during addiction as contrasted with abstinent periods. Moreover, the addiction and abstinence periods were quite distinct experientially and required separate analysis. Furthermore, the addicts in the study had committed over 500,000 crimes during an 11-year risk period. Theft was the main type of crime committed; other types of crime included drug sales and other crimes. Stepwise regression analysis showed that addiction was the principal force that increased criminality, regardless of the type of crime pursued. Findings support similar findings from other research and indicate that a major means of reducing the amount of crime committed by opiate addicts is to reduce the amount of addiction. Treatment programs targeted to specific offender populations are recommended, as is research that is accompanied by implementation efforts. Tables, figures, notes, and a list of 30 references are provided.