This paper studies the effect of the regional background of listeners on vowel perception. In Germanic languages such as English, German and Dutch, phonological descriptions of vowel systems distinguish between ‘long’ or ‘tense’ vowels on one hand and ‘short’ or ‘lax’ vowels on the other hand. Both categories may differ in pitch, intensity, vowel quality and duration. This paper focuses on the perceptual role of vowel duration in vowel categorisation. Durational measurements were made of unstressed Standard Dutch vowels in spontaneous speech samples of native speakers originating from Flanders (Belgium) and the Netherlands. Only for the Dutch listeners did vowel duration seem to be one of the parameters determining the location of the phoneme boundary between tense and lax vowels. For the Flemish listeners this boundary could not be determined on the basis of our stimuli.