PURPOSE In the randomized open-label phase III OVHIPEC trial, the addition of hyperthermic intraperitoneal chemotherapy (HIPEC) to interval cytoreductive surgery (CRS) improved recurrence-free and overall survival in patients with stage III ovarian cancer. We studied the cost effectiveness of the addition of HIPEC to interval CRS in patients with ovarian cancer. PATIENTS AND METHODS We constructed a Markov health-state transition model to measure costs and clinical outcomes. Transition probabilities were derived from the OVHIPEC trial by fitting survival distributions. Incremental cost-effectiveness ratio (ICER), expressed as euros per quality-adjusted life-year (QALY), was calculated from a Dutch societal perspective, with a time horizon of 10 years. Univariable and probabilistic sensitivity analyses were conducted to evaluate the decision uncertainty. RESULTS Total health care costs were €70,046 (95% credibility interval [CrI], €64,016 to €76,661) for interval CRS compared with €85,791 (95% CrI, €78,766 to €93,935) for interval CRS plus HIPEC. The mean QALY in the interval CRS group was 2.12 (95% CrI, 1.66 to 2.64 QALYs) and 2.68 (95% CrI, 2.11 to 3.28 QALYs) in the interval CRS plus HIPEC group. The ICER amounted to €28,299/QALY. In univariable sensitivity analysis, the utility of recurrence-free survival and the number of days in the hospital affected the calculated ICER most. CONCLUSION On the basis of the trial data, treatment with interval CRS and HIPEC in patients with stage III ovarian cancer was accompanied by a substantial gain in QALYs. The ICER is below the willingness-to-pay threshold in the Netherlands, indicating interval CRS and HIPEC is cost effective for this patient population. These results lend additional support for reimbursing the costs of treating these patients with interval CRS and HIPEC in countries with comparable health care systems.