Vietnamese-Australian women have infants with lower birth weight than Australian-born women. Traditional humoral food habits, based on ancient Chinese medicine, are more likely to be followed during life changes like pregnancy. These food habits may influence maternal energy intake, weight gain and therefore infant birth weight. This study determined the proportion of pregnant Vietnamese women in southwestern Sydney who practise traditional humoral food habits, and their effect on birth weight. A cohort of 113 pregnant Vietnamese-born women were questioned on smoking status, height, weight, parity, food practices and demographics. Dietary intake was measured in each trimester. Known risk factors and infant birth weights were collected from medical records for participants and nonresponders. Fifty-seven per cent practised the traditional food habits. There were no differences in energy intake or weight gain between the two groups. After adjusting for confounders, birth weight was estimated to be 3257 g (95 per cent confidence interval (CI) 3205 to 3309) and 3272 g (CI 3211 to 3333) for the infants of traditional and nontraditional women respectively. Following humoral food habits does not appear to affect birth weight. Women who choose to follow these traditions should not be discouraged from doing so.