Lead author Dr. M. Rosa Solorio of the University of California at Los Angeles AIDS Institute says interventions for the newly homeless -- who have been away from home for a period of between one day and six months -- have focused on addressing individual risk behavior and not on addressing structural factors, such as living situations, that might have an impact on their behavior.

Solorio tracked Los Angeles County homeless teens ages of 12 and 20 over two years and asked about depression, substance use, living situations, number of sexual partners and condom use.

At the beginning of of the study 77 percent said they were sexually active, but that percentage increased to 85 percent by the end of the period. Males were found to be more likely to have multiple sex partners if they lived in settings without family members, and abused drugs. For females, drug abuse was the primary predictor of risky sexual behavior, the study said.