The aim of this presentation is to measure to what extent long vowels are confused with diphthongs by Turkish English majors. A diphthong is made of two components. By definition and sound structure, diphthongs are a combination of two separate vowel sounds that, when uttered, the first vowel glides onto the second vowel forming a single syllable, as heard in /[long i], [ou], [long a], [oh], [oi]/. By nature, diphthongs happen to be long vowels. Long vowels, on the other hand, do not include two vowels that do not glide, as in /a:, i:, u:, [long u], [open-mid back rounded vowel], [open-mid central unrounded vowel]/. No vowel sound has a fixed length and many other factors affect length, such as the voiced consonant sound directly after a vowel sound will affect its length (voicing), reduction and intonation. It is said that to hear vowel sounds within words is easier than it is to hear the sound alone. Long vowels are generally said to be the easiest vowels for non-native English speakers to distinguish and hear correctly. This assumption will be tested with 30 instructors of English language education who are enrolled for MA degree at a foundation university in Ankara. The perception of long vowels vs diphthongs in written words and the audition of them in oral forms were measured within two separate applications of a pre-test and a post-test. It was discovered that the Turkish English instructors perceived the diphthongs (86, 3%) better than long vowels (73,3% ). It was deduced that the main cause of learning difficulty behind the diphthongs and long vowels, apart from L1 intervention, was the fact that Turkish learners of English suffer from a psycho-orthographic trauma created by the spelling of the diphthongs and long vowels by means of several letters.