In the community of P., a formerly severely endemic area of the Klatovy region, 213 school children (100 boys and 113 girls) aged 7 to 13 years were examined after more than 20 years of iodisation of table salt. The size and type of goitre was examined, height and body weight and urinary iodine excretion were assessed. The same examinations were made for comparison in 194 children (76 boys and 118 girls) in a Prague school, i.e. in an non-endemic area. The somatic development of the children from the endemic area, expressed as height and body weight, was retarded in relation to the development of children from Bohemia as a whole and in particular when compared with Prague children. In both groups only small diffuse goitres were observed or small nodular goitres, contrary to the period before the onset of iodisation when at that age medium-sized diffuse and nodular goitres were frequent. The difference in the prevalence of goitre in both groups was significant in 8-9-year-old children of both sexes. In girls it persisted to the age of 10 years, there was considerable nodulation. In boys from the endemic area goitre was found in 34.0%, in girls in 40.7%, nodulation was observed in boys in 14.0% and in girls in 18.7%, while in Prague the corresponding values in boys were 19.7% (and 3.9%, resp.) and in girls 20.3% (and 6.8%, resp.). The mean values of urinary iodine excretion varied in both areas and in the two sexes between 30.0 and 230.0 micrograms/l. Association revealed a statistically significant relationship between iodine excretion and the presence of goitre in boys and girls of the endemic area and boys from Prague. It was revealed that dietary iodine deficiency remains a permissive factor in the development of goitre and is more marked in former endemic foci. Prevention by iodised table salt protects newborn infants, but does not prevent the development of goitre in all subjects in the course of development of the organism. The possibility of reinforced iodisation in treated areas deserves consideration.