The aim of this chapter is to discuss the relation between sugars and dental caries. The prevalence of dental caries has declined during the last decades because of the habitual use of fluoride, but dental caries is still a common problem. Dietary sugars have an etiological role in caries: frequent consumption of sucrose and other fermentable carbohydrates increases the risk of the disease. There are differences between the different dietary sugars: Sucrose can be considered as the most harmful sugar, as it induces acid attack and serves as a substrate for sugar polymers important in dental plaque formation. Lactose, on the other hand, is not as cariogenic as many other dietary sugars. Despite the differences between the sugars, the role of an individual food component is never as important as the diet as a whole. Furthermore, caries is a multicausal disease: in addition to diet, e.g. home-care and use of fluoride are important in the prevention of dental caries.