A psychosomatic study was conducted with grade school and high school students to examine the occurrence of diarrhea and constipation in relation to their perception of illness. In order to find out in greater detail the nature of diarrhea and constipation and the awareness of illness in adolescents, a further psychosomatic study was conducted by questionnaires, psychological tests, interviews and somatic examinations. A follow up study was conducted two and a half years later. The main results were as follows. 1. The incidence of diarrhea and constipation increased significantly in so-called adolescence over the period from junior high school to senior high school. Boys had more diarrhea while girls more constipation. 2. Those who had only one bowel movement a day were found in 61 to 72% of the male population, while in only 50 to 69% of the female population. In regard to the type of stool, as many as 11 to 21% of boys and 11 to 24% of girls reported that they usually had soft, hard or sheepdung stools. As they were mostly healthy students, these findings suggest that the awareness of illness is an important factor in diagnosing irritable colon syndrome. 3. Significant interrelationship was proven to exist between the occurrence of diarrhea and/or constipation and sociopsychological factors such as anxiety, emotional unstability and social maladaptation. 4. Significant interrelationship was proven to exist between the awareness of illness and sociopsychological factors. 5. Almost 2/3 of the students who have diarrhea and/or constipation with the awareness of illness developed their first symptoms during the period of preparing for enter to the upper schools and/or for adjusting to the new school surroundings. Among their precipitating factors anxiety and tension in connection with school examinations were mentioned by 2/3 of the students. 6. About 2/3 of both diarrhea and constipation types showed a lymphoid hyperplasia in the part of terminal ileum by the X-ray examination. In the lactose tolerance test (50g), more than 80% of both types showed less than 20mg/dl of the maximum rise of blood sugar. However, there was no significant difference between these two types. 7. The. significant interrelationship between the occurrence of diarrhea and/or constipation and sociopsychological factors was supported by the follow up study which was carried out two and a half years later.