The study wants to find out the characteristics of pregnancies, deliveries and newborns with low birth weight (LBW)compared to the newborns with birth weight of 2500 g and more, in respect with the specific situation of twins.Records of antenatal clinics and maternity hospitals about 5500 children born within strictly given time limit of 16 months during the years 1991-2 to mothers with permanent habitation in Brno were evaluated.The children and their families have been participating on still running prospective longitudinal study ELSPAC aimed to finding the determinants of the healthy development.The low birth weight occured in 5.42 % of children.There were altogether 48 pairs of twins, the low birth weight occurred in 52.6 % of them. The mother of childrenwith low birth weight entered the prenatal care later, with less consultations, had more complications both during their pregnancies and the deliveries and their children showed more often different kinds of neonatal morbidity.The mothers of twins were suffering from anaemia and hypertension more often than mothers of single children.The research of the Brno newborn population shows the quantitative differences of risk that influenced the courses and the results of the pregnancies which ended by deliveries of children with low birth weight.Results are compared with those of children delivered with the birth weight of 2500 g and more.