A 3 years supervision of 415 pre-school children was undertaken in Paris from 1974 to 1977. Four epidemiological sets of questions provided information on the familial and social situation as well as on the physical and psychological development of the child at 3, 9, 18 and 36 months of age. A cluster analysis was applied to the behavior and health variables in the 3 year-old child and 3 different groups were identified. Most children (69%) belong to the first group, characterized by the absence of difficulties or the presence of a few minor symptoms, 10% of the children belong to the third group, a "high risk group" because of their high frequency of symptoms. Half-way between these 2 groups, a "low-risk group" (21%) was identified. The reliability of this analysis was further supported by the study of the families (especially their social and economic status and the parents' mental health). This study also revealed the early onset of the symptoms in high risk children.