The present study describes the histological features of enamel in teeth showing either mild or severe fluorosis. Sections were examined in transmitted and polarized light after imbibition in aqueous media or alcohols and quinoline. For semiquantitative study contour maps were prepared. Furthermore quantitative imbibition studies were performed along a traverse through the enamel and at selected points. From the values of total path difference, birefringence was calculated and imbibition graphs drawn. Finally, contact microradiographs were made. The study showed that it is only possible to correlate the degree of histological change with clinical features in severe cases of dental fluorosis. The general morphology of fluorosed enamel does not differ from normal enamel, but the tissue comprise areas of diffuse hypomineralization. In polarized light, opposite to microradiography, much more extensive changes were observed. Thus, slight degrees of dental fluorosis were recorded only when using polarized light. In severe cases, a maximum degree of 25% porosity or more were recorded and located immediately deep to a well-mineralized enamel surface. In severe cases of fluorosis, only dark zones were observed when examined in quinoline, and the quantitative imbibition studies showed that the enamel in these cases reacted similar to what is described in initial caries lesions. In both slight and severe dental fluorosis the subsurface porous region behaved as a ‘mixed body’ in aqueous media, but when examined in alcohols, these could only penetrate the tissue completely in severe cases. Thus, in mild dental fluorosis the subsurface region behaved as a ‘molecular sieve’. The findings in the present study are correlated to previous observations of enamel formation in order to explain the pathogenesis of dental fluorosis.