Epidemiological surveys have provided key information about the prevalence and degree of seriousness at different ages of a wide array of problem behaviors such as delinquency‎,‎ substance use‎,‎ early sexual involvement‎,‎ and mental health disorders‎.‎ Knowledge of the extent of these problems and changes in their course over time is important‎.‎ In its absence‎,‎ interventions and health planning in general can be difficult‎.‎ Understanding which risk and protective factors are relevant to which problem behaviors is also essential for the formulation of theories that constitute the basis of intervention‎.‎ This book draws on the results of the major Pittsburgh Youth Study complemented by follow‎-up tracking of juvenile court records for more than six years‎,‎ to address the following questions‎:‎ *What is the prevalence and age of onset of delinquency‎,‎ substance use‎,‎ and early sexual behavior for three samples of boys age 8‎,‎ 11‎,‎ and 14‎?‎ What are the average mental health problems for these ages‎?‎ How strong are the relationships among these problem behaviors in each of the samples‎?‎ *Which variables best explain individual differences among the boys in their manifestations of delinquency‎,‎ substance use‎,‎ early sexual behavior‎,‎ and mental health problems‎?‎ To what extent do explanatory factors vary with age‎?‎ How accurately can boys with different outcomes be identified by risk scores based on hierarchical multiple regressions‎?‎ *To what extent are explanatory factors associated with one outcome that are also associated with other outcomes‎?‎ Are explanatory factors that are especially characteristic of a multiproblem group of boys‎-‎-who display many different problem behaviors‎-‎-different from explanatory factors associated with boys with few problems‎?‎ *Do the results fit a general theory of juvenile problem behaviors‎,‎ or is a differentiated theory more applicable‎?‎