At study sites in Rochester (New York), Denver (Colorado) and Pittsburgh (Pennsylvania), three research teams studying the impact of family disruption on juvenile delinquency have interviewed approximately 4,000 participants at regular intervals for a decade, recording their lives in detail. Findings to date indicate that preventing delinquency requires accurate identification of the risk factors that increase the likelihood of delinquent behavior and the protective factors that enhance positive adolescent development. Overall, data indicate a consistent relationship between a greater number of family transitions and a higher level of delinquency and drug use. The magnitude of differences between youth with no family transitions and those with many transitions was similar across the three cities, and the relationships were statistically significant in Rochester and Denver. These findings have implications for the prevention and treatment of delinquency and drug use. (Contains 6 figures and 15 references.) (SLD)