Linear hypoplasia of the deciduous teeth is rare in most human populations, but common where nutritional status is poor. Deciduous enamel hypoplasia, hypocalcification, and hypoplasia-related caries are described in Middle and Late Woodland skeletal series from the Lower Illinois Valley. Gross enamel defects that can be referred to pre-natal development are found in 83 of 170 children under six years of age at death. Circular caries secondary to hypoplasia is significantly more common in the Late Woodland series, reflecting the apparent higher cariogenicity of Late Woodland diets. There is a significant association between prenatal dental defects and bony evidence for anemia and infectious disease. Children with enamel defects show relatively higher weaning age mortality than those without. These relationships suggest that at least moderate levels of malnutrition existed in Illinois Woodland populations.