BACKGROUND: Epidemiological studies of psychopathology in the first years of life are few, and the association between mental health problems in infancy and psychiatric disturbances later in life has not been systematically investigated. The aim of the present project was to study mental health problems and possibilities of intervention from infancy and onward.

METHODS: The basic study population consists of a birth cohort of 6,090 children born in the year 2000 in the County of Copenhagen, the Copenhagen County Child Cohort, CCCC 2000. At stage one CCCC 2000 was established on data from the Civil Registration System, Danish national registers, and standardized, longitudinal data from the first year of living obtained by public health nurses. At stage two a subsample was assessed at 1(1/2) years of age concerning child psychiatric illness and associated factors in a case-control study nested in the cohort, including a random sample. Participation rate at stage one was 92%.

PERSPECTIVES: Ongoing studies of CCCC 2000 include studies of failure to thrive, register studies, and studies of the predictive validity of public health screening. A follow-up study concerning the prevalence of psychopathology at age 5 is planned.

SUMMARY: The Copenhagen County Child Cohort CCCC 2000 is a longitudinal study of mental health from infancy investigating psychopathology in early childhood. Results from this study will add to the knowledge of risk factors and course of mental health problems in childhood and contribute to the validation of the mental health screening made by public health nurses.