This paper reports the results of an investigation on the types and frequencies of X-ray examinations given to patients with various types of their dental diseases from their first visit to the hospital to the end of treatment. The subjects were 337 patients (not including orthodontic patients and in-patients) randomly sampled out of all those who visited the Fukuoka Dental College Hospital in 1986. Out of these 337, the number of those who were given X-ray examinations was 284. 1. The Cases of dental diseases for which X-ray examinations were given were classified into the following seven: diseases caused by dental caries, trauma, inflammation, diseases of temporomandibular joint, diseases of salivary gland and other diseases, and other examinations. Out of these X-ray examinations, those given to the patients of diseases caused by dental caries and marginal periodontitis amounted to the 60% of the total X-ray examinations. 2. On the average, 3.3 radiographs were taken per patient. 3. In the examination of luxation, a case of trauma, 7.8 radiographs were taken per patient, the largest number of all diseases on this report. In the examination of marginal periodontitis, a case of inflammation, 5.4 dental radiographs and 0.5 panoramic radiograph were taken per patient. It is necessary to make the most of panoramic examination effective for this disease to decrease radiation exposure. 4. The diseases that have more difficulty of diagnosis and more necessity of observing the prognosis had a greater tendency to depend on X-ray examinations. 5. The percentage of the patients who did not receive X-ray examination was 15.7%. Out of these patients, the patients in pedodontics accounted for 34.5%.