Eleven pregnant patients with neurofibromatosis have been studied. They have had twenty-four pregnancies. Ten of these patients developed hypertension during their confinements. In the eleventh patient records were inadequate for analysis. In five of the ten patients, lesions of neurofibromatosis appeared for the first time during pregnancy. In the others the lesions increased in size and number. The lesions regressed considerably after delivery. It would seem that the hypertension during these pregnancies is more than a chance association.