The participants were all attending methadone maintenance treatment centers in Baltimore and New York City between May 1983 and April 1984. The 50 black and 50 white Baltimore participants were all consecutive admissions to five treatment centers; the 50 black, 50 white, and 50 Hispanic New York City participants were consecutive admissions to a single treatment center. All were at least 25 years old and had experienced their first period of narcotic addiction at least 2 years before the interview. The data they provided was factor analyzed, and results of the factor analysis were used to develop the typology. Numerical taxonomic methods produced nine types as well as a group that was uninvolved in crime. Among these types, the "violent generalists" were the most serious criminal offenders, were responsible for a disproportionate amount of violent crime, and tended to commit large amounts of different kinds of crime at high rates. Other types were the distributor-dealers, distributor-holders, distributor-tasters, thieves, gamblers, loan sharks, deceivers, and generalists. Tables, notes, and 27 references (Author abstract modified)