To determine whether oestradiol or follicle-stimulating hormone (FSH) measured prior to treatment could improve the predictive value of the risk score used to determine treatment in cases of persistent gestational trophoblastic disease (GTD). Prospective observational study. Tertiary referral centre for GTD. All women referred to Weston Park Hospital, Sheffield, with GTD between 1st January 1996 and 31st December 2000. Blood was taken prior to the initiation of treatment to measure oestradiol and FSH. The results were analysed with respect to the time taken for the beta-hCG to return to normal. Time taken to reach a normal beta-hCG. Data on 118 women were collected. Three women died of GTD during follow up. Using Cox's proportional hazards regression analysis, division of the risk scores into high and low risk groups (</=7, >7) demonstrated a significant difference with regard to the length of time taken to reach a normal beta-hCG level (hazard ratio 0.32; 95% CI: 0.18, 0.57) comparing high risk relative to low risk. However, addition of neither oestradiol nor FSH to the Cox regression analysis produced a significant hazard ratio (Ln oestradiol, 0.95; FSH 0.99). Division of the patients' risk scores into three groups of low (0-4), intermediate (5-7) and high (>7) risk groups produced similar results. The measurement of neither oestradiol nor FSH appears to improve the prediction of outcome in persistent GTD when added to the risk score.