objective: to determine the prevalence of dental fluorosis in primary school students of the department of caldas, colombia, in 2002. materials and method: a cross-sectional study to determine the prevalence of dental fluorosis in primary school students in the four regions of the department of caldas was carried out. a probabilistic sample was selected for the urban area and, arbitrarily, for the rural area. one thousand and sixty-one students were examined at their own schools, in daylight conditions and the dean index was applied. univariate and bivariate analyses were made with a chi-squared test being applied for the latter to show independence among variables. results: it was found that 63.3% (95% ci = 60.0-66.1) of primary school students in the department of caldas were affected by fluorosis in any degree of severity. among them, 56.3% (95% ci = 52-59) were classified in the mild and very mild degrees, while 7% (95% ci = 2-16) were classified in the moderate or severe degrees of fluorosis. a statistically significant association of the region variable with dental fluorosis was observed. however no association with the gender, area, schooling and age variables was found. the eastern region showed the lowest prevalence (47.9%) as compared to the other three areas (northern, center-southern and western), which showed prevalences above 68%. conclusions: two out of every three primary school students in the department of caldas suffer from a certain degree of dental fluorosis.