Objectives: To determine the serological status of the population in mainland France aged 1 to 6 years and 6 to 49 years with regard to measles, mumps, rubella, hepatitis A, hepatitis E, toxoplasmosis, herpes simplex virus type 1 and 2 (HSV-1 and HSV-2) infections, and cytomegalovirus (CMV) infections. Materials and Methods: Patients were enrolled during two surveys: children aged 1 to 6 years were included in 76 hospitals selected at random following a two-stage survey (Saturn-Inf survey), and individuals aged 6 to 49 years were included in 124 laboratories selected at random following a two-stage survey (Séro-Inf survey). Serological testing was performed by the same laboratory for both surveys. The estimates were weighted by survey weight and adjusted for age, sex, and region of residence of the individuals included in each of the two surveys. Results: 1,617 children aged 1 to 6 years (Saturn-Inf survey 2008–2009) and 5,300 patients aged 6 to 49 years (Séro-Inf survey 2009–2010) were included. The proportions of susceptible individuals for measles, mumps, and rubella were 10%, 15%, and 11%, respectively, among children aged 1 to 6 years; 8%, 14%, and 8% among individuals aged 6–29 years, and 1%, 6%, and 5% among those aged 30–49 years. The proportion of seropositive individuals among children aged 1 to 6 years was 3% for HAV, 1% for toxoplasmosis, 13% for HSV-1, and 0.3% for HSV-2; among those aged 6–49, it was 26% for HAV, 5% for HEV, and 38% for toxoplasmosis; it was 42% for CMV among those aged 15–49; it increased between the ages of 6–8 and 18–19 from 23% to 42% for HSV-1 and from 1% to 5% for HSV-2. Conclusion: The proportion of susceptible individuals to measles, mumps, and rubella among those under 30 remains high in France (7%), allowing for the occurrence of measles or mumps outbreaks. These results also suggest a decrease in exposure to hepatitis A and toxoplasmosis among people born after 1980. (R.A.)