The sample of 349 subjects was selected from a police roster of male narcotic abusers first known to the Baltimore City Police between 1952-1971. Time periods were established in 5-6 year groups beginning in 1952. Because a major emphasis was on the career patterns of addicts as they occurred over time, with race a major variable, the sample was weighted toward earlier time periods with equal numbers of whites and blacks. Data were drawn from interviews with addicts and the FBI's official apprehension records (rap sheets). The before-after comparison was based on selection of a fixed number of years and comparison for each addict of the crimes committed during that period before the first use of narcotics with the crimes committed after the onset of addiction. Methodological difficulties arose from the lack of comprehensive data regarding minors who were drug addicts and the necessity to partition the aggregate time into on and off narcotics periods (with correction for opportunity when in jail). In before and after comparisons of criminality, it was found that late and very late black starters show an increase in crime after narcotics addiction with an emphasis on property crimes. For late white starters, data are less reliable, but it seems that there is little difference in criminal activity between the before and after periods. Among early starters, 67.5 percent of the blacks had already begun first narcotic use. Comparisons of time on and off narcotics show that for both blacks and whites, criminal activity was considerably greater while subjects were actively taking narcotics. Concerning the popularity of types of crime, a slight increase in the proportion of violent crimes between the before and after periods was noted for whites, while for blacks, the proportion of violent crimes was much lower after the onset of addiction than before. Seven tables and 11 references are included.