The objective of the present study was to assess the diagnostic potential of serum human chorionic gonadotropin (hCG) ratios obtained at different intervals after evacuation of hydatidiform mole to diagnose persistent trophoblastic disease (PTD) and to compare its diagnostic accuracy with the current FIGO 2000 criteria as a gold standard. We calculated hCG ratios from serum hCG concentrations of 204 patients (86 with and 118 without PTD) registered with the Dutch Central Registry for Hydatidiform Moles between 1977-2004. The hCG ratios obtained in week 1, 3, and 5 after evacuation identified, respectively, 20%, 52%, and 79% of patients with PTD (median: 3.0 weeks) at the 95% specificity level, while FIGO 2000 criteria identified, respectively, 0%, 16%, and 66% (median: 4.7 weeks). It is concluded that a serum hCG ratio identifies patients with PTD approximately 2 weeks earlier than the internationally accepted FIGO 2000 criteria and identifies more than 75% of patients who develop PTD by the fifth week after evacuation.