Having addressed the problem of standard methods and comparability of epidemiological data and recognizing the problems which remain, at an intercountry level, even when data have been carefully selected, the Oral Health unit of WHO has been able to develop a global picture of dental caries prevalence and is constructing similar maps for periodontal diseases. Inevitably, the precision and representativeness of such data vary from country to country, but they are nevertheless invaluable for their intended purpose of providing a good approximation of disease prevalence and trends.It is clear that populations in highly developed countries almost always have high or very high prevalence of dental caries. It is even more striking that developing countries have or have had low to extremely low prevalence of the disease, but are suffering rapid and unmanageable increases in prevalence. At the same time, high to very high prevalence of periodontal diseases persists in all populations, though the problem seems to be greatest in developing countries.It is extremely disappointing and indeed tragic that this state of affairs can exist in 1976 when, for decades, we have had effective preventive measures available and have new methods appearing almost daily.The WHO oral health programme has given prevention its top priority position and its approach is based on the premise that we can and must implement the preventive methodology we have, to halt increases in dental caries prevalence, to reduce its prevalence and to control periodontal diseases.