Nurses who fail to identify knowledge gaps in their practice and who do not maintain competence place patients with cancer at risk for adverse events and poor outcomes. Self-assessment tools can assist oncology nurses in identifying knowledge deficits in fundamental oncology concepts. This article describes the development and implementation of a self-assessment tool to assist nurses in maintaining competence to provide safe, effective oncology care. The tool was developed after an examination of relevant literature, collaboration with an oncology team, and consideration of the Oncology Nursing Society's and American Nursing Association's standards of care. Preliminary evaluation suggests it may offer an effective means for oncology nurses to identify knowledge deficits and tailor educational interventions to address identified needs.