The conference on Physical Trauma as a Cause of Mental Retardation dealt with two major areas of etiological concern - postnatal and perinatal trauma. Following two introductory statements on the problem of and issues related to mental retardation (MR) after early trauma to the brain, five papers on the epidemiology of head trauma cover pathological aspects, terminal hemorrhages in the brain wall of neonates, postmortem neuropathologic findings in birth-injured patients, and epidemiological studies. Nine papers report perinatal studies on such topics as obstetric history, obstetric trauma, fetal head position, maternal pelvic size, birth position, intrapartum uterine contractions, and related fetal head compression and heart rate changes. Five special studies of the developing brain concern trauma during labor, trauma to neck vessels, the immature brain's reaction to injury, partial brain removal in infant rats, and cerebral ablation in infant monkeys. The following aspects of the premature infant are discussed in relation to MR in five papers: intracranial hemorrhage, CNS damage, clinical evaluation, EEG and subsequent development, and hematologic factors. Five papers on postnatal trauma examine subdural hematoma and its etiology, the battered child, an interdisciplinary prospective study, and intellectual sequelae of coma due to acceleration concussion. (KW)