In 7675 deliveries performed at the University of Messina between November 1, 1983 and October 31, 1988 we determined the incidence and obstetric factors specifically associated with the birth of very low weight infants (less than or equal to 1500 gm) (VLBW). Our purpose was to characterize these factors in order to determine what may be done to limit delivery rate of VLBW. Information obtained concerning the mothers' included socioeconomic status, age, parity, previous obstetric history, any maternal conditions affecting the pregnancy, route of delivery (vaginal or operative). The incidence of infants under 1500 gm was 1.1 per cent of live births. The etiologic analysis showed that preterm labor is more frequent cause of VLBW. In women under 17 years of age the incidence of VLBW was 5.2 per cent as opposed to 1.1 per cent in the total population. Absence of prenatal care was shown in 40.8 per cent of VLBW. The previous obstetric history reported 1 or more abortions in the 53 per cent and 1 or more perinatal deaths in 17 per cent of VLBW. The clinical implications of these results are discussed.