Many studies involving small animals have clearly shown that malnutrition affects tooth formation and causes increased dental caries. We have conducted two cross-sectional studies and one longitudinal study among Peruvian children to investigate the effect of early malnutrition on oral health. The cross-sectional studies have shown that in malnourished children the pattern of caries development as a function of age is significantly altered as a result of a delayed eruption and exfoliation of the deciduous teeth. This phenomenon has made difficult the observation by other scientists of a clear effect of nutritional status on total caries experience because the comparison of age-adjusted caries data between populations of children with different nutritional status is inappropriate. The use of peak caries activity has allowed the observation of a strong association between malnutrition and increased dental caries. The longitudinal study has confirmed the results of the cross-sectional studies and has demonstrated that one mild to moderate malnutrition episode occurring during the first year of life is associated with increased caries in both the deciduous and permanent teeth many years later.