Randomly selected groups of 486 Southern Chinese and 129 non-Chinese 12-yr-old Hong Kong children were examined for calculus and oral debris. The non-Chinese children had less plaque and calculus than the Chinese children (P less than 0.001). The girls had lower plaque scores than the boys in both ethnic groups. The higher frequency of toothbrushing by the girls possibly reflects their greater awareness of personal appearance. There is a need to increase the standard of oral hygiene and the level of dental awareness amongst Chinese children living in Hong Kong.