Haiti is the poorest and most heavily HIV-burdened country in the Western hemisphere, with even less health infrastructure than many countries of sub-Saharan Africa. Since the early 1980s the HIV epidemic has affected the poorest communities in Haiti, who lack access to even basic healthcare. Large-scale HIV treatment requires that basic healthcare services be built and scaled up simultaneously with HIV-prevention and -care programmes. Such improvement in access to general healthcare will require substantial investments in health infrastructure, service delivery and human development. This study describes the contribution of the non-governmental organization, Zanmi Lasante (ZL) to the HIV prevention and treatment scale-up and to the ongoing efforts to improve primary healthcare (PHC) services in the public health system in Haiti. The model depends on community health workers (CHWs) who supervise antiretroviral therapy (ART) and provide community outreach, including active case finding and outreach to marginalized populations. Zanmi Lasante has recruited, trained and financed a large cadre of CHWs to provide such linkages between communities and health centres in rural Haiti. The study analysed key components of their work--their self-perception, their role in enhancing community uptake of services and their role in targeting vulnerable groups. We found that most patients at risk were properly identified at a community level. The CHWs are facilitating the uptake of PHC services, including by the most vulnerable households. The general training of CHWs has created a positive self-definition in these cadres of their medical, patient support and health service roles; although with some variability across different groups. The results of this study will be used to emphasize, standardized and strengthen the biosocial training of CHWs.