The maintenance of good oral health is essential for nutrition, recovery and well-being. This requires the involvement of the nursing staff, especially in cases where oral care and any necessary dental treatment are vital to ensure medical treatment. The aim of this study was to evaluate the validity of oral assessments performed by nursing staff using the revised oral assessment guide (ROAG), using comparisons with patients' self-assessment of oral problems. When a comparison was made of how the staff and patients assessed their oral status, a high level of agreement was found. In these assessments, with the exception of oral mucosa and teeth, the percentage agreement was >80. The kappa coefficient revealed slight to moderate agreement. When there was a disagreement, the staff assessed the oral health as being significantly poorer than the patients did. In the present study, it was shown that few oral assessments performed by the nursing staff and patient disagreed. The ROAG may therefore be useful for the nursing staff to make the patients' oral health problems visible.