The prevalence and distribution patterns of enamel defects in maxillary incisors was assessed in 194 Singaporean children aged 11-15 years and belonging to three different ethnic groups. All were born and continuously resident in Singapore, which has a tropical climate. The water supply was fluoridated in 1957 at a level of 0.7 ppm. The mouth prevalence of defects was 71.5 per cent and the tooth prevalence was 55.9 per cent; 82 per cent of all affected teeth demonstrated white lesions of various forms. Although there was no sex difference in the prevalence and distribution pattern of defects, some racial differences were observed. The results were compared with data from other studies where the same classification of defects was used.