1. In medicine and dentistry, compliance tends to be poor in patients who have chronic diseases that they perceive as nonthreatening. 2. Even in the most optimistic studies, the rate of complete compliance with suggested toothbrushing is less than 50%; other studies show it much lower. In studies focusing on the use of interproximal cleaning aids, compliance is poorer still. 3. Patients in university-based programs have had a dropout rate (noncompliance) of 11% to 45%. In private periodontal practices, complete compliance was seen in one third or less of the patients. 4. The nature and the rate of disease progression affect SPT. The converse is also true. 5. In studies of the effect of therapy, it would be beneficial to record the results of treatment on all the patients, even those who drop out of therapy, to determine the part SPT plays in stabilizing the disease. 6. Patients fail to comply for many reasons, including self-destructive behavior, fear, economic factors, health beliefs, stressful events in their lives, and perceived dentist indifference. 7. By recognizing the problem, compliance can be improved in most patients. 8. There is a need for studies to define further the extent to which SPT affects the longevity of the dentition.