In examining youth admitted to juvenile detention centers and emergency crisis shelters, this study found that youth admitted to juvenile detention had proportionally higher levels of problem behaviors, such as substance use, than youth admitted to shelter services. However, both groups of youth had significantly higher levels of substance use than national estimates. The study also found that the most important risk factor for alcohol and marijuana use in both groups was the use of other substances. Research has documented that in addition to the risk for drug use being particularly high during adolescent years, runaway or homeless youth have an even greater risk for drug use. The study examined the risk factors in cigarette, alcohol, and marijuana use between runaway youth using runaway shelter services and youth admitted to juvenile detention for non-criminal behaviors. Specifically, the study sought to determine to what extent demographic and individual characteristics were different between runaway youth using shelter services and those admitted to juvenile detention; what demographic, individual characteristics and family factors predicted cigarette, alcohol, and marijuana use or non-use; and what factors predicted the level of cigarette, alcohol and marijuana use among these groups of runaway youth. Runaway youths were recruited from both service groups between 1999 and 2001. The study sample consisted of 121 youths from juvenile detention and 156 youths from emergency shelter. The study provides useful and beneficial information to service providers and policymakers concerning the substance use of runaway youth that utilize various service agencies. Tables, references