In the assessment of ethmoid disease we, the otolaryngologists, have few diagnostic precedures except physical examination and radiography. But the complexity of the arrangement of ethmoid air cells limits those diagnostic accuracy and usually presents a dilema in the evaluation of radiographic opacity of the ethmoid sinus. Recently applications of ultrasound to the evaluation of the maxillary or frontal sinus were reported as a useful diagnostic tool that is a simple, reliable and non-ionizing modality. Author applied diagnostic A-mode ultrasound to the ethmoid sinus through the orbit in the model experiments of water-immersed dry skull and in the clinical cases of normal subjects and patients of ethmoiditis. Author presents the echo findings in the model experiment and those of normal subject and of ethmoiditis as the clinical applications of diagnostic A-mode ultrasound to the ethmoid sinus through the orbit.