Homeless adults are at high risk for Hepatitis B virus (HBV), Hepatitis C virus (HCV) and HIV infection due to high rates of injection drug use and unprotected sexual activity. Our NIDA-funded RO1 award has enabled us to implement a successful intervention designed to evaluate the effectiveness of a HBV vaccination intervention with homeless adults. Our findings revealed that a greater percent of homeless adults randomized to the Nurse Case Managed Plus Incentive and Tracking group completed the HAV/HBV vaccine series compared to a Standard program without tracking. Homeless persons least likely to complete the vaccine series were young (< 40), and were men having sex with men (MSM); a significant number of these young adults also reported methamphetamine (MA) and cocaine/crack use. Stimulants (SAs), including MA and cocaine/crack are commonly used by homeless MSM, who contend with disorganized lives, unemployment, and little access to health and social services; thus, HBV vaccination is particularly challenging in this population. HAV/HBV vaccination and effective behavioral treatment are two of the most important strategies for reducing HBV infection among this at-risk group of SA users.