The departmental Maternal and Child Health (PMI) services are responsible for organizing health screenings in preschool for children aged 3–4. As part of this initiative, two surveys were conducted in 2005 and 2010 in the Hauts-de-Seine department, involving 1,914 and 1,227 children, respectively. For each survey, the following data are presented: sociodemographic characteristics, medical history, vaccinations, and the results of the clinical examination (including assessment for overweight) and screening for sensory, language, and behavioral disorders. The overall rate of referral to a specialist consultation is analyzed according to three vulnerability criteria: speaking a foreign language (29.9% and 36.6% of each sample, respectively), attending school in a priority education zone (12.1% and 13.6%), inadequate health insurance coverage (15.5% and 13.4%), and any combination thereof. Previous attendance at PMI center consultations increases very significantly whenever at least one vulnerability factor is present. Regarding the 3-4-year checkup, with the exception of vaccinations, health outcomes are stable between the two surveys, particularly the overall rate of referral to a specialist consultation (29.5% and 27.1%, non-significant difference, NS). Children with one and especially two vulnerability factors are referred more frequently (40% and 36.5%, p<0.001), as are children whose father is an employee or manual laborer (33.6%, p<0.001), but even in the most favorable situations, at least one in five children is referred. These results highlight the existence of social health inequalities as early as age 4, but also underscore the value of universal health screenings. Currently underutilized, the data collected during the 3- to 4-year-old health screenings in preschool could be used regularly on a broad geographic scale to guide and evaluate public policies and programs. (R.A.)