A survey was undertaken in 3 French departments of the Pays de Loire from January 1, 1986 to December 31, 1986. Among the 32,876 neonate (NN) population, the authors studied the 2,753 NN who were hospitalized and a control group of 1,458 NN representative of the population of 30,123 NN who were not hospitalized. Socioeconomic patterns of mothers, of their pregnancies and deliveries were studied in both groups. The control group was compared with the data obtained in 1981 at the national level and in 1982 at the local level. This group was used as a reference for the study of hospitalized NN. Intrauterine growth retardation rate was 2.4%, prematurity rate 4.6% of live births, very premature rate (as defined by a gestational age less than 32 weeks) was 0.45% of births. Among the group of hospitalized NN, which represent 8.5% of the general population, the NN were regrouped according to Cullen's classification and their care load estimated according to the Omega score. Thus 2 subgroups were defined: the 2,298 ordinarily hospitalized (Cullen's classes I and II) and the 455 severely sick NN (classes III and IV) i.e. 1.3% of births. One third of the severely ill NN were very prematures. The 2 other thirds presented with respiratory (24%), infectious (24%), malformative (19%) or neurological (13%) diseases. Lengths of stay and Omega scores varied according to the causes for hospitalizations and were inversely correlated with gestational ages (p less than 0.001). Neonatal mortality was 3.3 p. 1,000 births and rate of stillbirths 6.5 p. 1,000.