OBJECTIVE: Complete hydatidiform molar pregnancies occur in approximately 1 of 1,000 conceptions. After uterine evacuation of the trophoblastic tissue, women are followed up with serial serum human chorionic gonadotropin (hCG) measurement s. Patients are considered to have attained remission when their hCG level spont aneously declines to an undetectable level and remains there during a 6-month f ollow-up period. This standard effectively detects all disease recurrence; howe ver, it is resource intensive, delays child bearing, and is subject to significa nt noncompliance. Our objective was to determine the risk of disease recurrence after hCG spontaneously declines to undetectable levels. METHODS: We used a data base from the New England Trophoblastic Disease Center to analyzehCG levels in p atients with complete molar pregnancies. RESULTS: Among 1,029 women with complet e molar pregnancy and complete data, 15%developed persistent gestational tropho blastic neoplasia. The rate of persistent neoplasm among those whose hCG level f ell spontaneously to undetectable levels was 0.2%(2/876, 95%confidence interva l 0-0.8%). No women developed persistent gestational trophoblastic neoplasia a fter their hCG level fell to undetectable levels using an assay with a sensitivi ty of 5 mIU/mL (n = 82, 95%confidence interval 0-4.5%). CONCLUSION: Based on our experience with women with complete hydatidiform molar pregnancies whose hCG val ues spontaneously fell to undetectable levels after molar evacuation, we conclud e that the risk of recurrent neoplasm after hCG levels fall to less than 5 mIU/m L approaches zero. OBJECTIVE: Complete hydatidiform molar pregnancies occur in approximately 1 of 1,000 conceptions. After uterine evacuation of the trophoblastic tissue, women are followed up with serial serum human chorionic gonadotropin (hCG) measurement s. Patients are considered to have attained remission when their hCG level spont This standard effectively detects all disease recurrence; howe ver, it is resource intensive, delays child bearing, and is subject to significa nt noncompliance. Our objective was used to determine the risk of disease recurrence after hCG spontaneously declines to undetectable levels. METHODS: We used a data base from the New England Trophoblastic Disease Center to analyze hCG levels in p atients with complete molar pregnancies. RESULTS: Among 1,029 women with complet e molar pregnancy and complete data, 15% developed persistent gestational tropho blastic neoplasia. The rate of persi stent neoplasm among those whose hCG level f ell spontaneously to undetectable levels was 0.2% (2/876, 95% confidence interva l 0-0.8%). No women developed persistent gestational trophoblastic neoplasia a fter their hCG level fell to undetectable levels using an assay with a sensitivit ty of 5 mIU / mL (n = 82, 95% confidence interval 0-4.5%) CONCLUSION: Based on our experience with women with complete hydatidiform molar pregnancies whose hCG val ues spontaneously fell to undetectable levels after molar evacuation , we conclud e that the risk of recurrent neoplasm after hCG levels fall to less than 5 mIU / m L approaches zero.