To present updated national birthweight percentiles by gestational age for male and female singleton infants born in Australia. Cross-sectional population-based study of 2.53 million singleton live births in Australia between 1998 and 2007. Birthweight percentiles by gestational age and sex. Between 1998 and 2007, women in Australia gave birth to 2 539 237 live singleton infants. Of these, 2 537 627 had a gestational age between 20 and 44 weeks, and sex and birthweight data were available. Birthweight percentiles are presented by sex and gestational age for a total of 2 528 641 births, after excluding 8986 infants with outlying birthweights. Since the publication of the previous Australian birthweight percentiles in 1999, median birthweight for term babies has increased between 0 and 25 g for boys and between 5 g and 45 g for girls. There has been only a small increase in birthweight percentiles for babies of both sexes and most gestational ages since 1991-1994. These national percentiles provide a current Australian reference for clinicians and researchers assessing weight at birth.