An association between the incidence of osteo-dental fluorosis with age and sex was studied in 18621 residents of 73 villages of two tribal districts, Dungarpur and Udaipur of Rajasthan (India). The mean fluoride (F) concentration in drinking water sources of these villages varied from 1.0 to 6.1 mg/L. Out of 11205 individuals of Dungarpur and 7416 of Udaipur districts, 8090 (72.1%) and 2914 (39.2%) exhibited evidence of dental fluorosis respectively. The maximum incidence of dental fluorosis was encountered in the age group of 13-20 years and minimum in the age group of 5 to 12 years in both the districts. Regarding the incidence of skeletal fluorosis, 21 years of age revealed 27.6% in Dungarpur and 12.0% in Udaipur. Whereas 44 years showed maximum incidence of skeletal fluorosis, its minimum incidence was found in the age group of 21-28 years. Severity of fluorosis could be associated with the advancing of age and F concentration. Moreover, males showed relatively a higher incidence of dental and skeletal fluorosis compared to their counterparts. Chi square test revealed the association between the incidence of fluorosis with that of age and sex was non-significant except for dental fluorosis in Dungarpur district (p < 0.05). Those villages having almost same F level, showed a variable incidence of fluorosis because of frequency of F intake and duration of F exposure besides other determinants.