Sealants and xylitol have been demonstrated to prevent dental decay, but their effect has never been compared in the same study. Regular use of xylitol chewing gum during 2 or 3 school years was compared with application of occlusal sealants in a randomized study. The reliability of the clinical observations was controlled by examining the presence of dental decay in the same teeth from bitewing radiographs in a blind study. After 5 years, no statistically significant differences between the sealant and xylitol groups were found. The results were in line with the results from separate studies with sealants or xylitol. There were no great differences between the costs of the measures. The selection between the compared preventive measures has to be made on the basis of practical aspects such as caries occurrence, availability of personnel and other resources, opportunity costs, cooperation with schools, and other local conditions.