To ascertain the prevalence of childhood and adolescent atopic dermatitis in a Japanese population, we clinically observed the total body of 5 to 6-year-old children (994 cases), 7 to 9-year-old children (1,240 cases), 10 to 12-year-old children (1,152 cases), 13 to 15-year-old children (1,670 cases), and 16 to 18-year-old adolescents (2,159 cases). The examination was performed in the spring of 1994-96, when exacerbation of childhood and adolescent atopic dermatitis most frequently occurs in Japan. Atopic dermatitis was observed in 24% of the 5 to 6-year group, in 19% of the 7 to 9-year group, in 15% of the 10 to 12-year group, in 14% of the 13 to 15-year group, and in 11% of the 16 to 18-year group. The prevalence of atopic dermatitis in 9 to 12-year-old children was two times and in 18-year-old adolescents five times as high as in similar age groups examined 20 years ago.