A multitude of individual, familial, and environmental variables have previously been identified as contributing to the development of problematic sexual behaviors (PSB) and general conduct problems (CP) in youth. The majority of these studies have focused either on individual youth characteristics or parenting behaviors such as child maltreatment. Although researchers examining contributions to PSB and CP generally acknowledge the importance of the impact of the home environment on youth behavior, few researchers have included family characteristics of both parents and siblings in their analyses. Additionally, some factors that have been identified as having great importance in general juvenile delinquency, such as age at the onset of behavior problems, have been under-studied in youth with illegal sexual behavior literature. To address these gaps, the present study explored the salience of individual youth characteristics, home ecology variables (i.e., caregiver and sibling variables), experiences of child maltreatment, and age of onset of sexual and non-sexual problem behaviors in predicting the severity of CP and PSB in a sample of 286 male youths (ages 12-18) residing in residential programs to treat illegal sexual behavior. This study utilized a multi-method approach including self-report and archival clinical file review. Specifically, data sources include retrospective youth self-report on the: Multidimensional Assessment of Sex and Aggression (MASA); the Juvenile Sexual Offense Recidivism Risk Assessment Tool-II (JSORRAT-II); the Juvenile Sex Offender Assessment Protocol-II (JSOAP-II); the Psychopathy Checklist: Youth Version (PCL:YV); the Massachusetts Treatment Center Dictionary (MTCD), a modified version of the Child Sexual Behavior Inventory (CSBI); and an age-of-onset rating sheet (ARS) developed for this project. Factor analysis was employed to assist in the creation of theoretically and statistically coherent scales across the two methods, and hierarchical regressions were used to predict the severity of PSB and CP in this sample. Hierarchical regression analysis indicated that when controlling for other variables, higher levels of Sexualization and Callous/Low Empathy predicted higher levels of PSB severity. Moreover, Emotional Dysregulation and an older Age of Onset of PSB predicted greater severity of CP. These outcomes suggest that slightly different mechanisms may be related to the prediction of the severity PSB and general CP behaviors in youth with illegal sexual behavior. Although Home Ecology and early Age of Onset of PSB did not predict outcomes as hypothesized, Home Ecology together with Sexual Abuse, and Emotion Dysregulation were significant in the model predicting severity of PSB before entering other variables, suggesting possible mediation of those variables. Additionally, an earlier Age of Onset of CP and Home Ecology were significant in the model predicting severity of CP before entering other variables, suggesting possible mediation of those variables. This study grappled with questions of differences in the development and trajectories of PSB and CP as well as with problems of method variance in psychology research. These topics, as well as the future research directions and clinical implications for prevention, early intervention, and current treatment programs are discussed.