The Child Health and Development Studies are longitudinal studies of pregnancy and the normal and abnormal development of the offspring. Women who were membres of the Kaiser Foundation Health Plan entered the study in early pregnancy, and their children were examined frequently until the youngest child in the study was 5 years old. This is a more intensive follow-up than hitherto reported. Of the 19,044 live-born children, 163 had definite and another 31 had possible congenital heart disease; the crude incidence rates per 1,000 live births were 8.8 for definite congenital heart disease and 10.4 for definite plus possible congenital heart disease. The incidence rate of congenital heart disease was 7.9 percent among all stillborn fetuses subjected to autopsy and 10.2 percent among those in this group with autopsies evaluated as being detailed enough to detect heart disease. Among the live-born children with congenital heart disease, 21 died in the neonatal period and 22 died in later infancy and childhood; about half the deaths were judged to have been due to heart disease. About 30 percent of the children with congenital heart disease had associated severe anomalies of other systems. In the whole cohort, 50 children had diagnosed chromosomal abnormalities (2.63/1,000 live births) and about 30 percent of them had congenital heart disease. Among the group of 163 children with definite congenital heart disease, the diagnosis was made in 46 percent by age 1 week, in 88.3 percent by age 1 year and 98.8 percent by age 4 years.