Diphthongs in Čakavian and Štokavian speeches on the coast are referred to as ‘adriatisms’, which were developed due to Venetian influence. Diphthongs in the Čakavian dialect have several features – the second vowel in the diphthong is usually longer and they most often appear in the medial position, of which the first diphthong vowel represents a weak vowel. According to previous studies, the diphthongs /ie/ and /uo/ are present in three speeches of the island of Brač: Bol, Gornji Humac, and Pučišća. Based on the spontaneous speech of native dialect speakers of different ages, genders, and education, Biočina (2019) concluded that the frequency of diphthongs varies with age and town. For the purposes of this study, part of the corpora from the doctoral study of Biočina (2019) was taken, more specifically, recordings of the spontaneous speech of 45 speakers from Bol, Gornji Humac, and Pučišća. The auditory analysis has revealed that diphthongs do not appear only in dialectal words (eg. ʃaltuora, neʋierix), but also in words from standard Croatian (eg. studient, buolniʦi). Targeted words with diphthongs (ie and uo) were auditorily and acoustically perceived and verified. This was followed by a formant analysis (F1 – F3 from the middle stable part of vowels and from three points of the vowel trajectories). Gender differences in the usage of diphthongs were found, but age differences were recorded in Bol and Gornji Humac. Results also showed that male speakers from Gornji Humac were using very closed ie realization, while diphthong pronunciation in Pučišća was very open and fronted. In Bol, ie was defined as a very closed and back diphthong, and uo was the most fronted in Pučišća. Female speakers from Gornji Humac used the most closed and back realizations of ie, while speakers from Bol pronounced the most open and front ie. The results pointed at certain auditory and acoustic differences in diphthong realizations and distribution in three geographically close Čakavian speeches.