The occurrence of accidental ingestion/aspiration and preventive measures were investigated at Tokyo Dental College Chiba Hospital. In addition, the characteristics of accidents at our hospital were analyzed by surveying the awareness of accidental ingestion/aspiration to utilize the data for prevention. Accidental ingestion accounted for about 30% of accidents that occurred at our hospital in fiscal 2008, but all ingested items were naturally excreted, and no accidental aspiration occurred. Accidental ingestion most frequently occurred when dental restorations were removed. Inlays and crowns were most frequently ingested, and dentists with 5 to less than 10 years of clinical experience tended to be involved in these accidents. According to the results of the questionnaire, removal of restorations was perceived as the treatment least likely to cause accidental ingestion/aspiration. Moreover, dentists who always took preventive measures against accidental ingestion/aspiration accounted for only 40% or less on average. To avoid accidental ingestion/aspiration, repeated courses and individual instruction for repeaters and the establishment of a surveillance system along with manuals to manage the violation should be emphasized.