Weights of babies born in the Prince of Wales Hospital, Hong Kong, in its first 2 years of operation were studied, and compared with previous reports. Birth-weight in Hong Kong appears to have increased significantly in recent years. The method of data collection effects reference standards of birth-weight. The effect of different methods of data collection and statistical treatment of data for providing reference standards of birth-weight are discussed. In this series average birth-weight increased by 6.8 g per year of maternal age, 13.3 g per cm of maternal height, 42.5 g per previous baby and 104.9 g per week of gestational age; males were 110 g heavier than females. The effects of parity became significant at 35 weeks, and that of maternal age and height at 36 weeks; the effect of fetal sex was significant from 38 weeks onwards.