The purpose of this study was to assess the relationship of nutrition and dietary habits to gingivitis, dental calculus deposit and dental plaque adhesion in high school students. The subjects were 16 third-year students (7 males and 9 females) at a high school in Tokyo. Dietary investigation was made for 4 days from Sunday to Wednesday. Conditions of gingivitis and dental plaque adhesion were examined concerning the labial aspects of 6 anterior mandibular teeth and the condition of the dental calculus deposits of 4 mandibular incisors was examined with respect to their lingual surfaces, then index scores were given according to the severity. The results were as follows: 1) Investigation of nutritive intake revealed that intake of calcium, iron and vegetable in both sexes and intake of vitamins A and B2 in males were insufficient. 2) With regards to the regularity of meals, boys tended to have more unfavorable dietary habits compared with girls, namely, their frequencies of meals and eating between meals, and time of meal were more irregular. 3) The degree of gingivitis, calculus deposit and plaque adhesion were more severe in boys compared with girls. It was suggested that these serious conditions in boys resulted from improper nutrition and dietary habits. 4) A significant negative correlation was observed between the severity of gingivitis and the sufficiency rate of vitamin B2, light-colored vegetable and fat intake. 5) The results of assessing adequacy of nutrition and dietary habits showed that severities of gingivitis and dental calculus deposit were mild in the adequate group with significant difference from those in the inadequate group. 6) From the above, we can conclude that adequate nutrition and proper dietary habits are essential for the health of the periodontinum of high school students.