Preeclampsia is a pregnancy-specific syndrome manifested by de novo hypertension and proteinuria in the second half of pregnancy. The etiologic factors causing this disease are still not completely clear. The present study aimed to assess the morphological, histological and ultrastructural changes in the full term human placentae from pregnancies complicated by preeclampsia as opposed to those from the normal pregnancies and correlate them with the outcome of pregnancy. Fifty normal and thirty preeclamptic full term pregnant women were used in this study. After clinical assessment of all mothers, newborns, umbilical cords, and placentae, specimens from ten placentae of the preeclamptic women and the same number of placentae of healthy control pregnancies were taken & processed for both light and electron microscopic examination. The results of the clinical data showed no significant differences in maternal age, height, gravidity and parity between the two studied groups. However, the control women showed relative higher parameters regarding both maternal and gestational ages (28.1±6.1 year; 38.5±2.5 week) than those of preeclamptic patients (26.8 ± 5.8 year; 35.7 ± 1.0 week). Meanwhile, the preeclamptic women showed higher systolic and diastolic blood pressure (162 ± 10.3; 99.8 ± 4.04 mmHg) than those of the control women (111.4 ± 7; 71.9 ± 5.2 mmHg). The preeclamptic patients recorded lower values of the pregnancy outcome comparing those of the normal control women. The weight, length, head circumference, chest circumference and Apgar score of the preeclamptic newborns were, (2480 ± 233.6 gm; 46.300 ± 2.2 cm; 31.7 ± 1.5 cm; 30.2 ± 1.2 cm and 7.3 ± 0.9), lower than those of the normal control newborns (3365 ± 377.2 gm; 48.9 ± 2.8 cm; 34.12 ± 1.4 cm; 34.1 ± 1.8 cm and 9.9 ± 0.3) respectively. Moreover, the weight of the preeclamptic placentae (429 ± 63.5 gm) was less than those of the normal control women (590 ± 105.5 gm). However, the length of the umbilical cords of both groups was approximately equal. Light microscopy of samples showed multiple infarctions, excessive fibrinoid deposition within the intervillous space, increased stroma cellularity of the villi with endarteritis obliterans of their vasculature, increased number of the syncytial knots within the preeclamptic placentae. Transmission electron microscopy of the preeclamptic placental samples showed marked thickening of its syncytiotrophoblast cell membrane, loss of the microvilli, diminish number of mitochondria with dilatation and loss of their cristae, dilatation of the endoplasmic reticulum, vacuolization of its cytoplasm and marked changes of the nuclei with knot, sprouts and bridges formation. The endothelial cells of the preeclamptic villous capillary expressed various and severe alterations, consisting of swollen and bulbous cytoplasm, intracellular collagen deposition, few dilated mitochondria and thickening of its basement membrane. The capillaries exhibited thick wall and narrow lumen with clot formation. These changes could be the ultrastructural evidence of the placental ischemia with endothelial injury that presumed to be the pathogenesis of the preeclampsia.