The NCPP was a medical project conducted at a number of university-related hospitals for the purpose of collecting longitudinal medical and socioeconomic information on infants delivered at the hospitals, as well as data on the mothers and families. The Philadelphia sample included nearly 10,000 women who delivered their children at Pennsylvania Hospital between 1959 and 1965. The sample for the current study consisted of 987 individuals selected from the first 4 cohorts (1959-62) of 2,958 African-American mothers. Information collected through ages seven and eight encompassed medical, psychological, and sociological indicators. In the early 1980s a research team from the University of Pennsylvania collected information on school functioning and criminal history, including all police contacts, through age 17. In the summer of 1998, adult (beginning at age 18) criminal convictions through age 36 were obtained for those born into the 1962 cohort and age 39 for the 1959 cohort. The data analysis produced three key findings. First, males were more likely than females to be adult onset offenders. Second, participants with mothers who had smoked cigarettes during pregnancy were more likely to be adult onset offenders. Third, those who had higher scores on the total battery score of the California Achievement Test (CAT) were less likely to be adult onset offenders. The latter finding suggests that cognitive abilities may be a protective factor against adult onset criminal activity. The authors recommend that future research on adult onset factors have longer follow-up periods and draw on more official and self-report data. 5 tables, 4 notes, and 47 references