This study assessed the use of pit and fissure sealants by Ontario dentists, as well as variations in the knowledge and practices of this population with respect to certain aspects of the preventive technique. A mail questionnaire on dental practices and knowledge was answered by 1,276 general dentists in Ontario. Most dentists (90 per cent) provided sealants to their patients, and reported using sealants on an average of 45 per cent of their patients between the ages of six and 16 years. While most dentists knew that sealants have been proven effective in preventing caries (90 per cent), many incorrectly believed that sealants are cost-effective to apply to both primary molars and permanent premolars (40 per cent and 68 per cent respectively). Bivariate analyses showed that many of the reported characteristics are statistically significant. The variables that were consistently associated with sealant use include: knowledge of the effectiveness and cost-effectiveness of sealants; year of graduation from dental school; level of dental hygienist employment; and continuing education participation. Although multivariate analyses identified many of these variables as statistically significant, only a moderate amount of the variation in sealant use for patients aged six to 16 was explained (R2 = 0.22). Due to misinformation about the cost-effectiveness of sealants, some dentists may overuse them in certain instances. Conversely, misinformation about the effectiveness of sealants and the risk of further decay after sealant placement has resulted in some dentists under-utilizing them. Continuing education courses are needed to update dentists' knowledge and beliefs regarding dental sealants. In addition, dentistry's professional bodies should develop clinical practice guidelines to aid dentists in their treatment planning decisions.