The objective of this study was to determine if there were any demographic, behavioral, and clinical differences between clients seen aboard a mobile sexually transmitted disease (STD)/HIV clinic compared with those seen in a traditional municipal STD/HIV health clinic for receipt of STD/HIV services. Clients seen in the two different settings were interviewed about demographic characteristics, reasons for their visit, STD history, their HIV/STD risk factors, and the risk factors of their sex partners. Clients in both settings were also offered testing for syphilis, gonorrhea, chlamydia, and HIV. Results suggested that clients seen at the mobile clinic were older, more likely to be injecting drug users themselves and/or to have sex partners who were, or had engaged in prostitution for money or drugs. Over half (54.4%) of the mobile clinic clients sought testing for HIV, and they were far less likely to be seeking care for symptoms of an STD. In contrast, only 7.1% of municipal clinic clients indicated HIV testing as the reason for their visit, whereas nearly two thirds (64.5%) reported symptoms of disease. Two percent of municipal clinic clients and 5.4% of mobile clinic clients had a positive HIV test ( p<.001), and 17.8% of STD clinic clients and 5.6% of mobile van clients had a positive gonorrhea and/or test ( p<.001). These data suggest that a mobile STD/HIV clinic may be an effective strategy to reach individuals at high risk for HIV who are not being served by traditional municipal STD/HIV health clinics.