Preeclampsia has been suggested to result from a partial breakdown of tolerance to the developing fetus after maternal immune maladaptation. Several of the proposed immunomodulatory properties of the hormonal vitamin D system could potentially have beneficial effects for successful maintenance of pregnancy. Preeclampsia is characterized by marked changes in vitamin D metabolism. This paper reviews the evidence suggesting that the immunomodulatory properties of 1,25(OH)2D may play a key role in maintaining immunological tolerance in pregnancy, and proposes that ensuring adequate vitamin D status/intake may help in the prevention and management of preeclampsia.