The France Mission of Médecins du Monde aims to facilitate access to healthcare and rights for vulnerable populations within the general healthcare system, and to document their situation. The population served by its Reception, Care, and Referral Centers (CASO)—94.5% of whom are foreign nationals—lives in precarious conditions and is particularly affected by hepatitis B and C. Since 2000, a standardized social and medical record has been implemented in the CASO centers. The medical record includes information on serological status regarding HBV and HCV. Screening is offered to all new patients following an individualized prevention consultation. In 2014, the 20 CASOs received 28,517 different patients. Less than 24% knew their hepatitis status. Among French nationals, 58% were unaware of their status, compared to 78% of foreign nationals. For the latter, lack of awareness was more prevalent among the oldest and youngest age groups. Individuals from sub-Saharan Africa and Oceania/the Americas were significantly more likely to know their status compared to other foreign nationals. Length of stay in France was associated with greater access to screening. The HBV vaccination coverage rate among people over 15 years of age was low (26.9%), while it was higher among those under 15 (58.1%). Among the latter, the rate decreased as housing conditions deteriorated, but it increased with the length of stay in France and among children followed by maternal and child health services. Among patients screened at four CASOs in 2014, the prevalence of HBs antigen and anti-HCV antibodies was 8.6% and 4.3%, respectively. These results underscore the urgent need to develop specific prevention programs targeting migrant populations in precarious situations.