Previous data indicate that placentas from normotensive pregnancies in non-native women at 3100 m (Leadville, CO) are not hypoxic at term, despite lower uterine artery blood flow, than in the same population at sea-level. We hypothesized that placental vascular development is greater at 3100 m in compensation. Further, because the incidence of preeclampsia (PE), which has been linked to placental hypoxia, is 3-4 fold higher in this population, we investigated if preeclamptic placentas have altered vascularity compared to normotensive controls at 3100 m. Placentas from normotensive (NT) pregnancies at sea-level, 1600 and 3100 m, and late-onset preeclamptic placentas were collected at 3100 m. Placental and birth weights were determined, and stereology performed on paraffin- and resin-embedded tissue. Both normal and preeclamptic placentas at high altitude were smaller than those at sea-level, and birth weights trended down with no change in the placental index. Volume fractions of the placental and villous compartments were similar between all conditions, but the absolute volume of each compartment was reduced at 3100 m compared to sea-level. Villous volume was equivalent between sea-level and 1600 m. There were no differences between PE and NT placentas at 3100 m. Placental vascularity was similar at all altitudes, and the gas-exchange area was preserved at 1600 m but not 3100 m. Late-onset preeclampsia was not associated with placental changes at 3100 m.