In December 1990, 35 children in one kindergarten; 7,870 children in twenty-six primary schools and 2,657 students in three junior high schools in Kou-Hu, Ku-Keng and Szu-Hu Districts in Yunlin County, Taiwan, were examined by naked eye observation (NEO) for head louse infestation. The overall infestation rate was 16%. The infestation rate was highest in Kou-Hu (25%) and lowest in Ku-Keng (8%). The rate was higher among primary school children (21%) than among junior high school students (2%). The infestation rate of girls (34% in primary school children and 4% in junior high school students) was higher than that of boys (9%, less than 1% respectively). Among the primary school children the rate was highest in girls in grade 5 (39%) and boys in grade 4 (14%). The lowest rates were in girls in grade 6 (27%) and in boys in grades 5 and 6 (6%). In junior high school students, the rate of grade 1 (4%) was higher than those of grade 2 (less than 1%) and 3 (less than 1%).