Specialist nurses have existed for many years. Initially denoting a nurse with extensive clinical experience, implicit within nursing's professional agenda for attaining 'specialist' status since the 1960s has been the requirement to achieve a high degree of 'specialist' knowledge through post-basic education. Despite the professional agenda, much confusion surrounding definitions of specialist nurses prevails. In recent years this confusion has been compounded in the United Kingdom by the introduction of advanced nurse practitioners alongside existing clinical nurse specialists. This paper suggests that health care professionals' perceptions of a 'specialist' are subjective, grounded in their own experiences. Drawing on a study which examined relationships between paediatric oncology outreach nurse specialists and other health care professionals, two types of personal agenda from which perceived 'specialist' status evolves are described: (1) 'needs-driven agendas', and (2) 'peer-driven agendas'. When 'specialist' status is accorded to paediatric oncology outreach nurse specialists, 'specialist' knowledge is derived from: formal qualifications, hands-on technical skills, previous 'specialist' work experience, in-depth medical knowledge and/or insight into families' dynamics. The relative contribution each of these makes towards constructing a 'specialist' depends on the experiences of individual health care professionals and the varying work locations and professional backgrounds of paediatric oncology outreach nurse specialists.