The presence or absence of periodontal disease is determined by the equilibrium between the challenging microbial deposits, adhering to the tooth surface, and the host response of the individual patient. The possibility of affecting host response is limited. In primary prevention the main emphasis is therefore on the daily brushing of the teeth at home. The susceptible patient needs, in addition, suitable interdental hygiene measures. At school age, bleeding from more than three sextants of the dentition should be used as a sign of treatment need. Whenever calculus or other retentive factors prevent proper home care, secondary prevention, i.e. professional debridement, is indicated before oral hygiene instruction. Professional cleaning of the teeth at regular intervals has lately been found to greatly enhance the maintenance of periodontal health. Tertiary prevention of periodontal disease is the complex treatment of advanced periodontal breakdown. Recent research findings indicate that patients who have received treatment for advanced periodontal disease should, due to their initially poor host response, automatically be maintained in the high risk group and given meticulous professional cleanings as often as two to four times annually. The possibility of using chemotherapeutic agents for plaque control is limited to short term elimination of supragingival bacterial deposits. Mechanical oral hygiene is thus the method of choice in the prevention of periodontal disease. Regular surveillance of the patient's periodontal health is necessary for evaluation of the effect of such treatment.