Part of an international study of the nature and extent of childhood mortality in geographically, socioeconomically and culturally disparate populations, this report focuses on (1) an investigation into all deaths of children under 5 years of age, and (2) a probability sample of live children within the same northern California area during an 18-month period. For the Mortality Component, data are provided on mortality rates, description of the population, birth history of the deceased infants and children, prenatal care, circumstances of death, causes of death, and Sudden Infant Death. In the Probability Sample of Live Children, emphasis is on descriptions of both mothers of children under 5 years of age and children under 5 years of age. Major recommendations are offered for state and local health departments assuming responsibility for the stimulation, planning, and conduct of community-wide research on prenatal, infant, and childhood mortality on an individual case basis; and for international collaborative studies. Specific suggestions are made regarding data recording methods, health care delivery systems, methods of care for high-risk newborns, studies of Sudden Infant Death, childhood accidents, maternal education, and immunization programs. (LH)