Fluorosis levels and caries prevalence were evaluated in 152 children aged 6-8 yr residing from birth in an area with 5 ppm fluoride in the drinking water. Sixty-two of the subjects had mild fluorosis in both primary and permanent dentition, 31 were defined as moderate, and 4 cases had no signs of fluorosis; 14 cases had a more severe fluorosis level in the primary dentition as compared to 41 cases in which fluorosis was more severe in the permanent dentition. More primary dentitions were free of fluorosis in females than in males (P less than 0.05). No differences between males and females were found in the permanent dentition fluorosis. The decay rate in the permanent dentition gradually increased with increasing fluorosis severity, a finding not observed in the primary dentition. Reasons are discussed for the lower fluorosis level in the primary dentition and the more severe fluorosis in older age groups as well as the fluorosis severity difference by gender.