Although the enamel defects of low birthweight prematurely-born children have been well investigated clinically the ultrastructure has not been studied in detail. Using scanning electron microscopy this investigation examined the enamel surface of 4 representative teeth from a group of exofoliated teeth from prematurely-born, very-low birthweight children compared to an equal number of control teeth from normal birthweight children. The results showed that all 4 teeth from the prematurely-born group had enamel defects at the ultrastructural level even though the defects were evident only macroscopically in 2 teeth. By contrast all the control teeth from normal children did not show abnormalities of surface structure. Thus this investigation further confirms that birth prematurity and low birthweight adversely affect the activities of ameloblasts. Previous clinical investigations have reported that prematurely-born children show high prevalences of enamel hypoplasia of around 20-100%. The etiological factors involved in the pathogenesis of enamel defects are unclear, but are likely to be related to many systemic illnesses occurring during the neonatal period. These include respiratory distress syndrome, hyperbilirubinemia, maternal diabetes as well as neonatal rickets. Furthermore, Seow et al. (1989) showed recently that deficiency of calcium and phosphate mineral in the neonatal period is related directly to enamel hypoplasia in very-low birthweight, prematurely born children. In addition to systemic factors, local factors such as laryngoscopy and endotracheal intubation have also been implicated in the etiology of enamel hypoplasia in these children. While the enamel defects have been well studied at the clinical level, there is a paucity of information on the ultrastructural nature.(ABSTRACT TRUNCATED AT 250 WORDS)