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The peak Doppler-shifted frequency and degree of lumen narrowing were compared in 75 cervical carotid stenoses. Peak frequency was not found to precisely indicate severity of stenosis, but it was possible to divide stenoses into four ranges of severity on the basis of peak frequency. Peak frequencies of less than 5 KHz, in most instances, indicated stenoses of less than 50% decrease in lumen area. Frequencies from 5 to 8 KHz were generally associated with stenoses of 50–75% decrease in lumen area, and frequencies of 8–12 KHz were most often associated with stenoses of 75–90% decrease in area. Frequencies greater than 12 KHz almost invariably occurred in very severe lesions of greater than 90% decrease in lumen area (greater than 70% decrease in diameter). The use of peak frequency as an indicator of severity of stenosis, while not specific, is felt to be of considerable clinical benefit as it provides a more quantitative evaluation of stenosis than auditory assessment of Doppler frequencies.