Herpes gestationis, a rare vesiculobullous dermatitis of pregnancy and the postpartal period, can be more easily identified today thanks to recent immunologic and ultrastructural researches. Comparing two new case reports with the data provided by the literature, underlines the individuality of the disease, in spite of the analogies it shows with bullous pemphigoid. Clinically, the illness only appears during pregnancy or the postpartal period and generally responds well to vitamin B6. Histologically the bullae at the dermal-epidermal junction are accompanied by extra- and intra-cellular epidermal edema and vacuolation of the basal cells. Ultrastructural examination shows that the initial alteration affects the plasmatic membrane of the basal cells. The immunologic mechanism of the disease is specific as the usual indirect in vitro immunofluorescent methods cannot reveal factor B.