BACKGROUND: Despite improvements in the treatment of ovarian cancer, most patients develop recurrent disease within 3 years of diagnosis. There is no agreed second-line treatment at relapse. We assessed paclitaxel plus platinum chemotherapy as such treatment. METHODS: In parallel international, multicentre, randomised trials, between January, 1996, and March, 2002, 802 patients with platinum-sensitive ovarian cancer relapsing after 6 months of being treatment-free were enrolled from 119 hospitals in five countries. Patients were randomly assigned paclitaxel plus platinum chemotherapy or conventional platinum-based chemotherapy. Analysis was by intention to treat, except for toxic effects. FINDINGS: With a median follow-up of 42 months, 530 patients have died. Survival curves showed a difference in favour of paclitaxel plus platinum (hazard ratio 0.82 [95% CI 0.69-0.97], p=0.02), corresponding to an absolute difference in 2-year survival of 7% between the paclitaxel and conventional treatment groups (57 vs 50% [95% CI for difference 1-12]), and median survival of 5 months (29 vs 24 months [1-11). 717 patients developed progressive disease or died. The progression-free survival curves show a difference in favour of paclitaxel plus platinum (hazard ratio 0.76 [0.66-0.89], p=0.0004), corresponding to an absolute difference in 1-year progression-free survival of 10% (50 vs 40% [4-15]) and in median progression-free survival of 3 months (13 vs 10 months [1-5]). INTERPRETATION: Paclitaxel plus platinum chemotherapy seems to improve survival and progression-free survival among patients with relapsed platinum-sensitive ovarian cancer compared with conventional platinum-based chemotherapy.