Abstract: The invention relates to a method for quantification of a degree of obstruction in a liquid passageway, notably a male urethra. Data related to sonic waves generated by a liquid passing the obstruction may be accessed from a suitable file, or, alternatively may be directly obtained as a result of a measuring step 2. For determining the degree of obstruction of the urethra the measuring step 2 may be performed by arranging at least one sensor, notably a microphone, in the area of the perineum for detecting sonic waves generated by a liquid (urine) passing the obstruction. At the step 5 the power spectrum of the obtained data related to the sonic waves is calculated, after which a suitable feature 6a, 6b, or 6c representative of the power spectrum is selected. Preferable embodiments of the feature comprise a weighted average frequency of the power spectrum, a standard deviation of the power spectrum, or a skewness of the power spectrum, discussed above.