The onset of offending received much research attention in criminology; however, the majority of research focused on juvenile offenders. As a consequence, little was known about the prevalence of and causes associated with adult onset. Using data from the Philadelphia portion of the National Collaborative Perinatal Project followed through the mid- to late thirties, this study focused on the prevalence of adult onset and the factors related to adult onset. Three key findings emerged from this study. First, females were less likely than males to be adult onset offenders. Second, participants who had mothers that smoked cigarettes during pregnancy were more likely to be adult onset offenders. Third, participants who had higher scores on the total battery score of the California Achievement Test (CAT) were less likely to be adult onset offenders. Limitations and future research directions are outlined.