Peritonsillar infections include cellulitis and abscess (quinsy). Clinical diagnosis is often supplemented by diagnostic drainage (aspiration or incision) in an effort to distinguish abscess from cellulitis. In a prospective study of 14 patients we have shown that clinical impression alone is unreliable (sensitivity 78 per cent, specificity 50 per cent). Computerized tomography (CT) (sensitivity 100 per cent, specificity 75 per cent) and intraoral ultrasound (sensitivity 89 per cent, specificity 100 per cent) are much more reliable. We propose that intraoral ultrasound could play a useful role in the clinical assessment of peritonsillar infections helping to improve accuracy in distinguishing abscesses from cellulitis.