Background: The World Health Organization recently defined the criteria for constructing birth weight curves using population based data. Aim: To construct a national curve of weight, size and ponderal index at birth for Chile, following the criteria suggested by the World Health Organization (WHO) expert committee report from 1995. Material and methods: A national database from the Chilean Institute for Statistics was used. All alive singleton deliveries during the period from 1993 to 2000 were included. A birth weight curve for the total population as well as for size and ponderal index at birth was construted, including percentile distribution, mean and standard deviation of values for gestational age. Stratification by sex was performed. Results: A total of 2,049,446 singleton deliveries were analyzed. The 10 percentiles (raw data) for birth weight throughout gestation from 22 to 42 weeks were: 470, 520, 560, 630, 660, 749, 810, 926, 1,031, 1,160, 1,320, 1,480, 1,680, 1,920, 2,190, 2,500, 2,750, 2,910, 3,010, 3,080 and 3,090 g, respectively. Conclusions: A national birth weight for Chilean population (a predominant Hispanic population) was constructed. There are not differences between this curve and the standard proposed by WHO (population from California, USA) suggesting that under comparable perinatal indices, ethnicity is not a relevant factor determining birth weight (Rev Méd Chile 2004; 132: 1155-65)