Hydatidiform mole, a disorder of fertilization, comprises complete and partial molar pregnancy. The pathologic and clinical features of complete and partial mole are well-described. Because of earlier diagnosis, however, the clinical presentation of complete molar pregnancy has significantly changed in recent years. The earlier diagnosis of complete mole is associated with more subtle pathologic findings than later molar pregnancy. The use of immunohistochemical techniques for the detection of maternally imprinted genes as ancillary testing in the diagnosis of complete and partial mole is therefore increasing. Although most molar pregnancies are sporadic, a familial syndrome of recurrent hydatidiform mole has been described. Further research will hopefully lead to identification of the gene defect responsible for this uncommon syndrome. Fortunately, patients with molar pregnancies can generally anticipate normal future reproduction. Close hCG follow-up after molar pregnancy is required to rule out development of postmolar gestational trophoblastic neoplasia. Recent studies suggest that a shorter period of postmolar follow-up may be reasonable for patients with both complete and partial molar pregnancy.