Summary•Oral care is a basic nursing activity central to patient comfort and well‐being, the prevention of infection and the maintenance of nutritional status.•This care is particularly important in cancer when both disease and treatment cause significant destruction of oral membranes/teeth, marked decline in salivary secretion and increased risk of infection. Systemic infection, originating in the mouth, is regarded as a significant cause of death. Appropriate oral care is, therefore, an important part of cancer care.•Thorough assessment is required to: provide baseline data, monitor response to therapy, identify new problems as they arise.•Although several assessment guides have been reported, for the majority no reliability/validity data are available.•This paper describes evaluation of the reliability, validity and clinical usefulness of three such guides. All were found reliable with regard to detection of gross abnormalities although precision with regard to scoring of subcategories was less reproducible.•In terms of validity, the literature supported the assessment categories of all tools, although an expert panel, supported by the nursing observers, identified many inappropriate descriptors and omissions highlighting, in particular, the difficulty of selecting appropriate descriptors when differences were observed in different areas of the mouth.•The lack of reliability and validity limits the clinical usefulness of these tools; it also suggests that reservations must be expressed about research based on their use. Further work is required to develop suitable tool(s) for assessing oral status in