Use of a health diary has been common in nursing practice settings. Nurses have incorporated the diary as a means of helping clients to document their symptoms and factors which may have precipitated them, often with the aim of modifying particular health behaviours. To date there has been limited exploration of this tool in a nursing research context. Advantages and disadvantages associated with the diary when utilized as a research instrument in health settings are summarized and particular consideration is given to their use in nursing research with cancer patients. Features of the method such as completion and respondent co-operation, format and issues surrounding data analysis are considered. The advantages of this method warrant further exploration in nursing research, despite conflicting and insubstantial evidence regarding the feasibility, validity and reliability of specific kinds of information reported in a diary.