The purpose of the study was to describe variations in cognitive/behavioural changes during the course of delirium among older Taiwanese patients after elective surgery. A total of 106 patients assessed four times (admission, onset of delirium, delirium day 3 and delirium day 5) by the Mini Mental State Examination (MMSE) were included in the analysis to understand the neurocognitive/behaviour change during the course of delirium. Repeated measures anova was used to analyse within-subject differences across these four time points for those who became delirious and those who did not. The findings showed that patients who experienced delirium had significantly (P < 0.01) lower MMSE scores than non-delirious patients. Scores for the delirious group were also significantly different across the four assessments (P < 0.01) within the group. The subscales of orientation to time, orientation to place, registration and recall were the major changes from time 1 (admission assessment) to time 2 (onset of delirium) for delirious patients. When scores for time 4 (delirium day 5) and time 1 (admission assessment) were compared, the subscales of orientation to time, orientation to place and visual construction showed the least improvement among the subscales at time 4. The findings of the study suggest that mental status assessments are important during the patient's admission and hospital stay. The repeated assessments can be incorporated into routine nursing care so that problems can be detected and appropriate nursing care implemented.