The purpose of this study was to examine the status of periodontal disease in young female students, and to estimate the reliability of a screening method using CPITN in a large population. A primary examination of 1444 female junior and senior high school students was conducted in Sendai. The upper first right and left first molars, upper right first incisor, lower right and left molars and lower first left incisor were selected as the index teeth. Forty three subjects (approximately 3% of all students examined) who had CPITN values of more than 13 or who had one or more code 4 teeth were selected for secondary examination at the Dental Hospital of Tohoku University. Periodontal pocket depth, bleeding index and the presence of calculi were determined. A third examination was conducted on 36 students to measure alveolar bone loss using full mouth radiographs. The prevalences of both code 1 and code 2 were approximately 80% in each high school grade. The prevalence of code 2 increased with age and decreased in proportion to those of code 0 and code 1. The results of the primary examination were in 100% agreement with those of the secondary examination for code 0, 65.5% for code 1, 71.1% for code 2, 66.1% for code 3, and 33.3% for code 4. Slight or moderate alveolar bone loss was observed in all of the students who underwent the third examination, suggesting that they were suffering from mild to moderate periodontitis. In conclusion, the periodontal examination using CPITN was reliable for primary screening of large populations.