The pattern of horse fly (Diptera: Tabanidae) distribution and correlations among biodiversity, abundance, abiotic factors, and altitude were determined along a two-sided altitudinal transect. The sampling was carried out on five 3-d periods during tabanid seasonal activity. Linen canopy traps with 1-octen-3-ol as an attractant were used at 20 sampling sites along the transect. The results showed that the qualitative composition of tabanid species can be distinguished by altitude and, especially, between southeastern and northwestern mountain slopes. The peaks of horse fly species richness and abundance were indicated at middle elevations of both slopes, where horse fly distributional groups were overlapping and most rare and infrequent species were sampled. All expected species were sampled according to species accumulation curve. The canonical correlation analysis separated species and sampling sites into three clusters; two were positively correlated with the temperature and the wind but differed in sensitivity toward them, and the third cluster was correlated with the humidity. The horse fly distribution was nonhomogenous, and the distributional patterns were only partially determined by altitude and vegetation. The determining environmental variables were different for each slope: temperature and wind for the southern slope (Mediterranean climatic zone) and humidity for the northern slope (continental climatic zone).