OBJECTIVE to compare the clinical and morphological parallels of the mother-placenta-fetus system in diffuse toxic goiter (DTG) through current morphological examinations. METHODS Sixty-five women whose pregnancy occurred with DTG were examined using both clinical and morphological studies (light, scanning electron, and atomic-force microscopies and macro- and microelement analysis); the placenta and uterus were investigated. RESULTS Destructive changes and microrelief impairment, resulting from circulatory disorders (ischemia) and hemic hypoxia, were observed in the presence of DTG during pregnancy. Abnormal placental immaturity developed; the number of terminal villi decreased; sclerosis occurred. The magnitude of changes showed up to a greater extent in the myometrium, umbilical cord, and placenta of women, whose pregnancy occurred with DTG, and in patients with disease recurrence. In preeclampsia, plethora, stasis, and thrombosis were added to circulatory disorders. CONCLUSIONS Not only the diagnosis itself of DTG, but also the type of its course and the pattern of obstetric disease, primarily preeclampsia, affect the state of structural components of the uteroplacental unit.