The aetiological factors in enamel defects of a non-fluoride nature can be divided into systemic and local. The systemic factors comprise a variety of conditions: genetically determined, chromosomal anomalies, congenital defects, inborn errors of metabolism, neonatal disturbances, infectious diseases, neurological disturbances, endocrinopathies, nutritional deficiencies, nephropathies, enteropathies, liver diseases and intoxications. The genetically determined enamel defects include amelogenesis imperfecta, which may occur as an isolated phenomenon or as part of other disorders such as epidermolysis bullosa, pseudohypoparathyroidism and taurodontism. The congenital defects include heart disorders and unilateral facial hypoplasia and hypertrophy. Among the inborn errors of metabolism are: galactosaemia, phenylketonuria, alkaptonuria, erythropoietic porphyria and primary hyperoxaluria. Neonatal disturbances are important in the development of enamel hypoplasia, foremost among these are premature birth and hypocalcaemia. The latter causes postnatal hypoplasias, which, however, are never seen in breast-fed children. Haemolytic anaemia, mostly in conjunction with erythroblastosis foetalis, may cause enamel hypoplasia. In children with neurological disturbances a rather large number have enamel hypoplasias, and these changes may be a significant aid in neurological diagnosis. When the tetracyclines were introduced, many children had these drugs prescribed in the period when the teeth were undergoing mineralization. The result was a yellow-brown stain of the affected teeth. In recent years, however, there appears to have been a reduction in the incidence of tetracycline staining. As for local causes the most important are traumatic injuries and periapical osteitis of primary teeth.