The paper presents the study design of the development and organisation of an EU/WHO multicentre study on the promotion of children's early psychosocial development through primary health care services. The aim of the programme is to develop training for primary health care workers (PHCWs) that improves their ability to assess factors relevant to psychosocial development and gives them preventive approaches to foster that development, building on families' strengths. The focus is on the period from conception to the end of the second year of the child's' life. Two main components are the training of the PHCWs and the semi-structured interviews that guide the workers in practice. The training has content and structure that is feasible within primary health care resources working in collaboration with mental health services. The programme is evaluated in terms of (a) the impact of training on both the PHCWs' knowledge and attitudes with regard to infant behaviour and development, and on practice as assessed by the delivery of the semi-structured interview; and (b) the effect of the intervention on maternal well-being, infant language development and behavior, home environment and mother-infant interaction. The programme is taking place in Cyprus, Greece, the Federal Republic of Yugoslavia, Portugal, Slovenia and Turkey.