The prevalence of developmental defects of enamel of 1,417 Cook Island children aged 9-20 years on the island of Rarotonga was recorded in 1987. The labial surfaces of the 12 anterior teeth were examined and classified using the modified Developmental Defects of Enamel Index (DDE). At least 1 tooth with defective enamel was seen in 403 (28.4 percent) of subjects; 7.1 percent of all teeth were affected. These results show overall an intermediate prevalence in comparison with studies in other countries. The three most prevalent defects were: diffuse patchy opacities (2.4 percent of all teeth), demarcated white-cream opacities (1.6 percent), and hypoplasias (1.2 percent). The upper central incisors were the teeth most frequently affected. The prevalence of defects did not differ by age or sex. Most defects (40 percent) were located over the incisal third of the labial surface, and affected less than one-third of the labial tooth surface (76 percent).