Peritonsillar cellulitis and peritonsillar abscess are similar clinical entities with markedly different methods of treatment. Therefore, accurate diagnosis is paramount to appropriate treatment. This pilot study was designed to evaluate the sensitivity and specificity of intraoral ultrasound as a noninvasive method of differentiating abscess from cellulitis. Sixteen consecutive patients suspected of having peritonsillar abscess were prospectively evaluated with intraoral ultrasound. The results were confirmed with imaging or surgical drainage. Correct diagnoses were made in 9 (90%) of 10 abscesses and in 5 (83%) of 6 cases of cellulitis. Our results suggest that, while there is a learning curve for intraoral ultrasound, it is an accurate, noninvasive, and inexpensive tool to differentiate abscess from cellulitis. We believe that this will be a clinically useful technique in the future.