Objective: The purpose of this study was to determine the rates and predictors of HIV testing and receipt of results among homeless adults with serious mental illness in the initial 3-month period after contact with a community-based case management program. Method: Baseline and follow-up interview data came from clients (N=5,890) in the Access to Community Care and Effective Services and Supports program, and 18-site, 5-year federally sponsored demonstration designed to evaluate the effect of service system integration on outcomes for homeless persons with serious mental illness. Results: Overall, 38.0% of clients were tested for HIV in the 3 months after program entry; of these, 88.8% returned to receive their test results. Likelihood of being tested was independently associated with having been tested before, more severe psychiatric symptoms and drug problems, level of worry about getting AIDS, younger age, less education, minority status, longer-term homelessness, being sexually assaulted, being arrested, and health services utilization. Among those tested, likelihood of receiving the test results was higher among those with a history of prior testing and return for results, a higher frequency of testing, and more years of education and lower among those with drug abuse problems, outpatient medical service utilization, disability, and sexually transmitted disease. Interaction analyses showed that, for men, greater social support increased the likelihood of both HIV testing and receipt of results, while sexual victimization during follow-up decreased the likelihood that men would return for their HIV results. Conclusions: The majority of homeless clients enrolled in an intensive case management program were not tested for HIV during the 3-month period after program entry. Among those tested, however, nearly 90% reported receiving their results. The findings may enhance the development and targeting of strategies to increase testing and awareness of HIV serostatus among high-risk mentally ill homeless persons. (Authors)