Objective: This report provides descriptive longitudinal findings over three waves of a study designed to assess the development of antisocial behaviors in young and early adolescent Puerto Rican children at two sites. Method: Through the use of standard assessment measures, representative samples of Puerto Rican children of both genders 5 to 13 years of age and their adult caretakers were interviewed at two sites: the South Bronx in New York City (n = 1,138) and the Standard Metropolitan Areas in Puerto Rico (n = 1,353; N = 2,491). Results: Although no differences in prevalence between the two sites were apparent at baseline, analyses of the longitudinal data show that site differences emerge over time, with a decrease in risk of antisocial behavior over time in the Standard Metropolitan Areas relative to the Bronx. Conclusions: The decreased risk of these disorders in the Standard Metropolitan Areas corroborates the low rates in Puerto Rico reported in previous research. Future analyses of these data are needed to identify the risk and protective factors associated with this difference. (Contains 4 tables and 1 figure.)