The Kostel dialect (Slovene: kostelsko narečje [kɔsˈtéwskɔ naˈɾéːt͡ʃjɛ],[1] kostelska belokranjščina,[2] kostelščina;[3] Serbo-Croatian: kostelsko narječje), in Croatian literature also eastern microdialects of Western Goran subdialect (Serbo-Croatian: zapadni goranski poddijalekt, zapadni gorskokotarski poddijalekt, Slovene: zahodni goranski govori, zahodni gorskokotarski govori),[4] is a dialect spoken along the Kupa Valley in Slovenia and Croatia, around Banja Loka and Brod na Kupi.

[5] The dialect originates from Alpine Slavic, a predecessor of modern Slovene, but speakers living in Croatia self-identify as speaking Croatian.

It extends from Kuželj and Gornji Turni in the west, south to Ravna Gora, as far east as Razdrto, and north to Banja Loka and Kostel.

Notable settlements include Kuželj, Guče Selo, Brod na Kupi, Krivac, Gornji Turni, Kupjak, Ravna Gora, Skrad, Brod Moravice, Lokvica, and Šimatovo in Croatia, and Vas, Fara, Kuželj, and Potok in Slovenia.

[11] The Kostel dialect lost the difference between high- and low-pitched accent on both long and short vowels, which are still differentiated.