The fundamental objective of the proposed study is to develop and test an innovative two-stage, cross-systems family-based intervention for substance abusing juvenile offenders. The first stage of the experimental treatment is provided for youths in juvenile detention settings. Stage two of the intervention occurs after the offender is released to the community. Participants are randomized to one of two study conditions: the cross-systems family-based intervention (Multidimensional Family Therapy-Cross Systems (MDFT-CS), or 2) Enhanced Services as Usual (ESAU). Both conditions incorporate HIV prevention in detention and we will also examine the effects of a family-based HIV/STD prevention module beyond the impact of a standard HIV/STD education intervention delivered in detention by including ongoing HIV/STD intervention in MDFT-CS following release from detention. There are five aims of the proposed study. These aims relate to: 1) Intervention development and implementation; 2) Clinical effectiveness; 3) Impact of HIV/AIDS/STD prevention; 4) Comparative benefit-costs; and 5) Systems-level impact