This paper describes the estimated prevalence of dental caries and periodontal disease in 2,550 children, 5 through 17 years of age, who resided in five southwestern states of the United States and were examined in the Hispanic Health and Nutrition Examination Survey (HHANES) of 1982-84 of the National Center for Health Statistics. Dental caries in the Mexican American children was predominantly a disease of occlusal surfaces of molars; few smooth surfaces of posterior and anterior teeth were affected by caries. This intra-oral distribution of dental caries strongly supports the use of fissure sealants as a preventive procedure. Filled tooth surfaces contributed about 66 per cent of the total DMFS (decayed, missing, filled surfaces) scores. The analysis also shows that about 50 per cent of the 17 year old Mexican Americans had five or more filled or decayed teeth. Mild gingivitis was prevalent (76.9 per cent) in the Mexican American children.