The aim of the study is to demonstrate that intrapatient dose escalation of carboplatin would improve the outcome in ovarian cancer compared with flat dosing. Patients with untreated stage IC-IV ovarian cancer received six cycles of carboplatin area under the curve 6 (AUC 6) 3 weekly either with no dose modification except for toxicity (Arm A) or with dose escalations in cycles 2–6 based on nadir neutrophil and platelet counts (Arm B). The primary end-point was progression-free survival (PFS). Nine hundred and sixty-four patients were recruited from 71 centers. Dose escalation was achieved in 77% of patients who had ≥1 cycle. The median AUCs (cycle 2–6) received were 6.0 (Arm A) and 7.2 (Arm B) (P < 0.001). Grade 3/4 non-hematological toxicity was higher in Arm B (31% versus 22% P = 0.001). The median PFS was 12.1 months in Arm A and B hazard ratio (HR) 0.99; 95% confidence interval (CI) 0.85–1.15; P = 0.93. The median overall survival (OS) was 34.1 and 30.7 months in Arms A and B, respectively (HR 0.98; 95% CI 0.81–1.18, P = 0.82). In multivariate analysis, baseline neutrophil (P < 0.001), baseline platelet counts (P < 0.001) and the difference between white blood cell (WBC) and neutrophil count (P = 0.009) had a significant adverse prognostic value. Intrapatient dose escalation of carboplatin based on nadir blood counts is feasible and safe. However, it provided no improvement in PFS or OS compared with flat dosing. Baseline neutrophils over-ride nadir counts in prognostic significance. These data may have wider implications particularly in respect of the management of chemotherapy-induced neutropenia.