The aim of this study of Medieval Portuguese vowel sequences isthe study of vowel sequences in the Cancioneiros and otherMedieval Portuguese documents. The phonological status of thesevowels is defined as hiatus or diphthongs. All data have beensubmitted to auto-segmental and metrical analyses, with particularreference to the general phonological structure of MedievalPortuguese, according to the litterature.In the metrical approach, only the vocalic element can occupy theNucleus position.In falling diphthongs, all types of glides are analysed as Codaelements. Finally, it is necessary to note that MP has a significativeamount of ambissyllabic sequences of vowels.