This investigation was first, to assess the oral health of 11-year-old children in four ethnic groups in Amsterdam; second, to assess their dental behaviour and third, to identify potential determinants of frequency of toothbrushing. Representative samples of 97 Surinamese, 209 Moroccan, 128 Turkish and 102 Dutch children were examined orally and asked to complete a questionnaire. Results showed that Turkish and Moroccan children had higher mean DMFT and DMFS scores than the Surinamese and the Dutch children. The mean plaque scores in the Turkish and Moroccan children were higher than those in the other two groups. Large differences in frequency of toothbrushing were found between the four ethnic groups, the Surinamese and Dutch children claimed to be the more regular brushers. Logistic regression analysis showed that the frequency of toothbrushing was related to the children's attitude towards toothbrushing and not to parental influence.