This is a follow-up study to "Delinquency in a birth cohort", the 1972 study which traced the development from birth to age 18 of male delinquents in the Philadelphia birth cohort of 1945. This study follows a sample from the original cohort up to age 30 and extends the analytic strategies of the previous work. More than 60 per cent of the subjects were interviewed at age 25. Their attitudes, values, experiences as crime victims, self-reported involvement in crime, and other facets of their lives are used to round out the picture developed from official sources. Among their findings, the authors show that : there is little offense specialization, even during adult years; that the seriousness of offenses increases with age, but that the actual number of crimes committed decreases. In other aspects -- such as the intervals between arrests and differences between white and non-white arrest patterns -- the adult data sometimes replicate juvenile results and sometimes offer new insights into offender patterns.