To assess whether a complete hydatidiform mole (CHM) carries an increased risk of later requiring chemotherapy in pregnancies continued to term. The Charing Cross gestational trophoblastic neoplasia (GTN) database was screened between 1973 and 2002 to identify registered singleton CHMs with a known gestational age at the time of evacuation. Of the 8,313 cases 2,800 were centrally histopathologically reviewed by us and confirmed as CHM. The proportion of patients requiring chemotherapyfor both total registered and centrally reviewed patients was analyzed by trimester of evacuation (< 13, 13-24, > 24 weeks). Statistical significance was assessed by the chi2 test. For the total population, including non-centrally reviewed patients, evacuation occurring in the first, second or third trimester was associated with a treatment rate of 13.9% (601 of 4,333), 10.8% (412 of 3,803) and 5.1% (9 of 177), respectively. In patientsfor whom a central pathologic review had been performed to confirm the diagnosis, the treatment rates were 27.7% (525 of 1,897), 27% (241 of 893) and 20% (2 of 10). The higher apparent treatment rates reflect an error in the denominator as we do not review all nontreated cases. In the total population, evacuation in the third trimester correlated with a reduction in risk of subsequent treatment (P<.001). Most of these late deliveries were induced (before adequate ultrasound), whereas the earlier pregnancies were mostly terminated via suction dilatation and curettage. There is no evidence that delayed evacuation/delivery of singleton CHM increases the risk of subsequently requiring chemotherapy.