Background: Women with endometrial or ovarian cancer experience a variety of symptoms during chemotherapy. Patient-Reported outcomes (PROs) can provide insight into the symptoms they experience. A PRO tool tailored to this patient population can help accurately monitor adverse events and manage symptoms. The objective of this study was to identify items in the National Cancer Institute’s measurement system Patient-Reported Outcomes Version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE®) appropriate for use in a PRO tool for a population of women with endometrial or ovarian cancer undergoing treatment with taxanes (paclitaxel or docetaxel) in combination with carboplatin. Methods: A two-phase, sequential multi-methods approach was applied. In phase one, a comprehensive literature search was done to map the toxicity of the applied chemotherapeutics and phase III clinical studies. Phase two, which comprised selecting the PRO-CTCAE items, included discussions with and feedback from a patient advisory board, an additional literature search, and focus group interviews with senior oncologists and specialized oncology nurses. A national expert panel facilitated both phases in terms of carefully select items from the PRO-CTCAE library. Results: Phase one identified 18 symptoms and phase two, three additional ones, leading to the inclusion of 21 PRO-CTCAE symptoms in the final PRO tool. Since PRO-CTCAE also contains one to three sub-questions on the frequency, severity, and interference with daily activities of symptoms, there were 44 potential items. Conclusions: This study describes taking a multi-method approach to selecting items from the PRO-CTCAE library for use in a population of women with endometrial or ovarian cancer undergoing chemotherapy. By systematically combining diverse approaches, we carefully selected 21 clinically relevant symptoms covered by 44 items in the PRO-CTCAE library. Future studies should investigate the psychometric properties of this PRO tool for women with endometrial or ovarian cancer.