The pinworm prevalence among 302 children tested in 1980 in five Southern California elementary schools was determined to be 11.6%. The range was 7.3–15.4%. In a 1982 study involving 158 children in six schools, the prevalence was 21.6% (range 11.1–38.9%). The results of these studies are compared with those of a similar prevalence study done in the same area and in some of the same schools during the 5-year period 1960–1964. The prevalence for the earlier period, involving 700 children in six schools, was 34.6%, and ranged from 29.2–43.0%. A new, flexible, plastic pinworm slide was used in the 1980 and the 1982 studies. In the 1982 study, this diagnostic method was evaluated and compared for efficiency and use against the standard cellulose tape/glass slide. The two are equally effective in picking up eggs, and in reading quality. The plastic slide is easier to use and does not break.