The Collaborative Perinatal Study was designed to examine prospectively the broad problem of perinatal wastage with a particular focus on relationships between perinatal events and organic neurological defects of the offspring. Between January 1959 and December 1965, a total of 55,908 women in 14 hospitals were enrolled in the study. Although more than 500 publications have already appeared reporting special studies within the project, this is the first major report from the study. The report begins with a description of the design, population, procedures, protocols, and data-processing procedures of the study and then presents the data describing the characteristics and conditions of the pregnancies studied and the relationships of these characteristics to the pregnancy outcomes. Maternal characteristics such as marital status, age, education, cigarette smoking, height, weight, prenatal care, associated diseases; characteristics and complications of labor and delivery are analyzed. Perinatal wastage is divided into stillbirths, neonatal deaths, birth weights