Background: 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 and methods: 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). Results: 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. Conclusions: 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.