Background: The most important determinant of birth weight is gestational age. However, other biological variables may influence this parameter. Aim: To study the influence of maternal parity, height and neonatal gender on the birth weight of normal newborns in a public Hospital of Southern Chile. Material and methods: A computer registry of all deliveries attended in Temuco Hospital between 1993 and 1998 was analyzed. Normal deliveries giving birth to newborns of more than 2,500 g and from women who did not suffer from conditions that could influence birth weight, such as hypertension, undernutrition or smoking, were selected. Results: From 27,736 deliveries, 12,580 were selected for the study. Male newborns with gestational ages from 37 to 42 weeks, had a higher weight than their female counterparts. Multiparous women and those with a height over 154 cm gave birth to newborns with a higher weight than nulliparous women or than those with a height of less than 154 cm. Conclusions: According to these results, birth weight must be corrected by gender and maternal features, to define those newborns that have a low birth weight for their gestational age.