In order to analyze whether ultrasonography with a reasonable degree of confidence can replace radiography in the diagnosis of sinusitis, 138 patients with clinical signs of sinusitis were examined with both methods. It was found that maxillary sinus fluid was recognized ultrasonographically with a confidence that increased with the amount of fluid, judged from radiographic examinations. In a sub-group of 45 cases, fluid confirmed by maxillary sinus puncture was detected by ultrasonography in 35/45 sinuses (78%) and by radiology in 38/45 sinuses (84%). In patients with radiographically normal maxillary sinuses, the correlation to ultrasound was good. However, mucosal swelling and polyps or cysts observed at radiography were poorly demonstrated by ultrasonography. In addition, the ultrasound method was not reliable for frontal sinus diagnosis. It was concluded that ultrasonography can be recommended in maxillary sinusitis for follow-up of treatment and as a screening method before sinus radiography.