Evidence has emerged which challenges the original concept of periodontal disease on which the present approach to treatment has long been based. There is reason to consider the possibility that there is more variation in susceptibility to disease and tooth loss as a result of disease throughout the population than has been previously accepted. Many of our conclusions as to the need for and validity of particular treatment procedures have been based upon evidence from studies which have assumed relatively even distribution of susceptibility to disease throughout the population. This text reviews the treatment needs and the validity of the use of various techniques in the light of present knowledge.