High vowel weakening is a common phenomenon that usually depends on purely phonetic factors. This study aims to present the findings of an experiment we have conducted on a total of 14 native speakers to see if Turkish has high vowel weakening and if yes, to figure out whether it is phonological or phonetic. Our data show a large amount of variation and little correlation between a vowel’s F1 and its duration within the high ([+high], /i, u, y, ɯ/) and non-high ([-high], /a, e, o, ø/) categories in all environments (stressed and unstressed, in open and closed syllables, in all consonantal environments). On the other hand, comparing the duration of [+high] and [-high] vowels reveals that non-high vowels are rarely as short as, or shorter than, high vowels. However, this shortening process is not a purely phonetic phenomenon. What matters for this process to apply is the phonological category of the vowel. All [+high] vowels are shortened, largely irrespective of variation in their F1; conversely, [-high] vowels are not shortened, largely irrespective of variation in their F1.