Early detection in the framework of secondary prevention is an important task, although not the only one, of youth health care, 'the preventive and socio-medical complement of curative medicine'. The primary aim of youth health care is 'promoting and protecting health, growth and development of children and youths'. Periodic health examinations (PHE'S) are an effective and efficient mean to this end. Like all medical consultations PHE is characterised by the integration of its two components: the analysis which focuses on the individual child and its environment (history and physical examination) and the synthesis (general health education and specific counseling). Moreover PHE provides the basis for epidemiological research, collective health education and policy-planning. Complementary examination of a child, usually less extensive than PHE, is executed on the basis of an individual indication. For practical reasons groups of children may be examined in screening-programs. It is preferable to incorporate screening results in the total medical assessment, which is the result of a series of individual PHE'S. Fractionated and isolated screening-programs are not in accordance with the intrinsic value of youth health care. Therefore an integral approach of the child and its environment demands the maximum incorporation into the PHE of systematic and standardized methods of examination. The concept of the 'group at risk' threatens to supplant the search for the 'child at risk'. Collective health education programs are supplementary to individual counseling and health education, but cannot replace the latter.(ABSTRACT TRUNCATED AT 250 WORDS)