With the growing demand for cancer care in Australia, dominant models of nursing care are limited in their capacity to meet patient needs equitably. Currently, nurses lack a valid means to identify patients with complex care requirements who typically require specialist nursing intervention. Without such a tool, patients at greatest risk of sub-optimal outcomes may ‘slip through the cracks’. Nurses also lack a valid means to specify the case mix of specialist cancer nurses, ensuring that their expertise is directed to the patients who most need it. This project, funded by the Cancer Nurses Society of Australia, set out to develop and test the clinical relevance of a nurse sensitive complexity index for use with cancer patients in ambulatory care settings. 100 cancer nurse coordinators from across Australia contributed to the development of the index and iterative rounds of pilot testing. This paper will describe the rationale behind and the process involved in developing the index; present and discuss the final version, and describe a multi-centre study protocol to test the safety and clinical utility of the index in a Victorian study to commence in 2017.