A prospective study was carried out to evaluate the sensitivity of sonography in the diagnosis of peritonsillar abscesses (quinsy). From 1986 to 1991 all cases of clinically doubtful peritonsillitis were subjected to B-Mode ultrasonography of the tonsils before tonsillectomy. 118 patients were examined. Sensitivity of the method in cases of clinically uncertain peritonsillar abscesses was 87%. The predictive value of the method was calculated to be 0.89; however only five false positive cases ("abscess" in ultrasound but no pus during surgery) were found. We therefore suggest that all patients suffering from questionable peritonsillitis should be examined by ultrasound. If abscess formation is suspected, surgical intervention is indicated. In all other cases I.V. antibiotics should be administered and control sonography should be carried out.