Midmorning urine samples were collected from 623 first- and second-grade children in four elementary schools. The mean for water F content in the residential area from which the population was drawn was 0.024 ppm (55 samples). The mean urine F concentration for all subjects was 0.42 ppm (SD = 0.22). There were no significant differences in urine F levels as a factor of sex or age. Children living in the area for no more than 1 year excreted significantly higher levels of F in the urine than did the longer-resident youngsters. This is attributed to their probable exposure to higher F levels in drinking water prior to moving into this low-F area. The urine F mean was 17.5 times that of the drinking water F. Urine F measurements, therefore, cannot be taken as indicative of F content of drinking water when the concentration in water is very low.