The study included 985 cases of Hydatidiform mole. 262 of which needed chemotherapy due to malignant transformation or invasive mole. i.e.24.6%. It was noticed that malignant transformation was associated clearly with group of factors like advanced age, low socioeconomi states, multiparity, increase of uterine size more than gestational age, the size of the uterus, the presence of ovarian Lutein cysts, recurrent vesicular mole, evacuation, of Hydatidiform mole without suction, operetve interference especially laparotomy, grade of differentiation of vescular mole. it was also found that there is increase of malignant tranformation in thos women who used medical barrier contraceptive methods more than those who used hôrmonal contrceptive methods Knowing these risk factors helps in early diagnosis and treatment of those high risk. cases and decreases the incidence of malignant transformation.