The dental ages of 149 children born and grown up in a district with naturally occurring fluoride in the drinking water (maximum level 2.0 mg/1) were compared with those of 181 control children born and grown up in a neighbouring low-fluoride district (≤0.1 mg/1). The children were 9–12 years old. In neither group did the dental ages prove to differ from normality. It is concluded that concentrations below the highest recommended level fluoride occurring naturally in the drinking water do not seem to have any long-term effect on the individual physiologic maturation, as judged from the dental age of the growing child.