A total of 3604 dipteran species of 94 families have been established in the investigated mountains so far. Family Tachinidae is the most numerous (297 species), followed by Agromyzidae (255 species) and Mycetophilidae (244 species). The greatest number of species have been found in the Stara Planina Mts. (1723 species) and the mesophilic and xeromesophilic mixed forests belt (2525 species). The faunistic similarity between the mountains and the vegetation belts is scrutinised. The established species belong to 140 areographical categories, divided into two main groups: 1) species with Mediterranean type of distribution (247 species or 6.9% of all Bulgarian dipterans) – more thermophilic and distributed mainly in the southern parts of the Palaearctic and the low parts of the mountains; 2) species with Palaearctic and Eurosiberian type of distribution (3281 species – 91.0%) – more eurybiontic and more widely distributed in the Palaearctic and mountains. The endemic species are 76 (2.1%). The distribution of the areographical categories in the mountains and the vegetation belts is analysed.