This paper provides a summary of baseline prevalence data obtained in the National Preventive Dentistry Demonstration Program with 24,428 children in grades 1-8 from ten sites across the country. These data indicate that a large percentage of children had relatively low levels of dental decay in permanent teeth. The attack rate increased with grade so that by the eighth grade, about 90 percent of the children had one or more teeth involved. The difference between nonfluoridated and fluoridated attack rates also increased with grade level. At both types of sites, occlusal surfaces were most likely to be attacked, followed by buccal-lingual, and then proximal. The preventive power of water fluoridation was most apparent on the proximal surfaces. About 50 to 60 percent of the surfaces affected were filled, while almost all others were carious; i.e., there were very few teeth missing due to decay. It was further observed that there was considerable variation in the level of caries attack across sites. This was true for both fluoridated and nonfluoridated communities.