Demographic and epidemiologic changes that have occurred in the last five decades in many developing countries and that are characterized by major growth in the number and proportion of middle-aged and elderly persons and in the frequency of the diseases that occur in these age groups. The health transition is the result of efforts to improve maternal and child health via primary care and outreach services and such efforts have been responsible for a decrease in the birth rate; reduced maternal mortality; improved preventive services; reduced infant mortality, and the increased life expectancy that defines the transition. (From Ann Intern Med 1992 Mar 15;116(6):499-504).