THE INFLUENCE OF GENDER, LOW BIRTH WEIGHT, AND DISADVANTAGED ENVIRONMENT IN PREDICTING EARLY ONSET OF OFFENDING: A TEST OF MOFFITT’S INTERACTIONAL HYPOTHESIS STEPHEN G. TIBBEITS East Tennessee State University zyxw ALEX R. PIQUERO Temple University National Consortium on Violence Research zyxw Little is known about the causes of an early onset of offending. In an attempt to shed light on this issue, some theoretical models have been advanced purporting to explain the reasons for an individual’s early initiation into offending. In one of these models, Moffitt (1993) predicts that early onset of offending is caused by an interaction between (1) increased risk for neuropsychological disorders and (2) disadvantaged childhood environments. This study tests Moffitts hypothesis concerning the development of early offending. In the pres- ent analysis, low birth weight was used as a proxy for increased likeli- hood of neuropsychological deficits, and socioeconomic status and family structure served as indicators for disadvantaged environment. Using the Philadelphia portion of the Collaborative Perinatal Project, we find support for Mofitt’s hypothesis that neuropsychological risk and disadvantaged environment interact to produce an early, but not late, onset of offending. In subsequent analysis, the interaction was observed for males but not females. The latter result, however, may be a function of the small number of cases in the female sample. Finally, we address the theoretical and policy implications arising from our analyses and provide some suggestions for future research. Similar to the observed strong and positive relationship between past and future offending (Gottfredson and Hirschi, 1990; Nagin and Paternos- ter, 1991; Paternoster et al., 1997; Robins, 1966, 1978; Wilson and Herm- stein, 1985), the age at which a first offense occurs (i.e., onset) is an important factor in predicting the future offending of individuals. Studies have consistently found that early onset is one of the best predictors of serious, high-rate offending in adolescence and adulthood (Blumstein et al., 1986; Dunford and Elliott, 1984; Elliott et al., 1984; Farrington, 1986; Farrington et al., 1990; LeBlanc and Frechette, 1989; Loeber and LeBlanc, CRIMINOLOGY VOLUME 37 NUMBER zy 4 1999 843