text: A retrospective instrument has been designed (index cases, with sib and non-sib controls) for record-anchored Study of Mental Retardation (cases selected from Georgetown (G.T.) University Hospital Speciality Clinic) as a pregnancy outcome. Ten hypotheses were being tested, related to the biological and psycho-social mechanisms underlying the occurrence of damage in the growing white child by age 5 years: anoxia, toxic influences on brain, metabolic influences, trauma to the head, infection of brain, dehydration of child, genetic or familial factors, socio-economic status, prematurity, and nutrition. Heart disease, prenatal hypertension, breech presentation, bleeding, Cesarean Section (C.S.) and Cephalopelvic Disproportion (C.P.D.), were noted more frequently in mothers of M.R.; and meconium, B.W. less than 2500, and neonatal head injury more frequently in M.R. children themselves, than in the corresponding sib and non-sib controls. Findings from G.T. data base are being compared to findings from prospective Collaborative Perinatal Research (COLR) data base, using the same retrospective instrument. In view of less incomplete data in the latter, this comparison would confirm or invalidate the initial findings from the former.