Anxiety and salivary cortisol were measured in two groups of patients with recurrent aphthous ulceration. One group of patients had persistent aphthae (Group 1) and the others had been relieved of their aphthae following correction of detected haematinic deficiency states (Group 2). Anxiety was measured using the Hospital Anxiety and Depression scale and radioimmunoassay of salivary cortisol. There was a statistically significant increased proportion of borderline or clinically anxious patients in Group 1 compared to Group 2 (P < 0.05). Median salivary cortisol levels also showed a statistically significant elevation in Group 1 (P < 0.01). It is concluded that stress may play a role in the aetiology of recurrent aphthous stomatitis, particularly in patients who have an underlying anxiety trait.