It was the goal of this paper to compare the intensity of occurrence of fungal diseases on the leaves, ears and the base of the culm in spring barley in case of pure and mixed sowing using the conventional and organic method under the mountain conditions of the area of Beskid Niski in southern Poland. The research was conducted in the years 2013-2014 at the Mountain Experimental Station in Czyrna Niżna, located in the western part of the range of Beskid Niski. The conducted research had indicated varied intensity of the emergence of fungal diseases of spring barley depending on the studied factors. Spring barley grown using the organic system was characterised by a significant reduction in the intensity of prevalence of barley scald (Rhynchosporium secalis), fusarium ear blight (Fusarium spp.) and fusarium foot rot (Fusarium spp.). At the same time, this growth system had shown an increase in the intensity of barley stripe (Pyrenophora graminea) and barley net blotch (Pyrenophora teres). Under the prevailing natural circumstances, in all analysed zones of the hill side, the growing system did not have a significant influence on the index of infection of the culm foot by Oculimacula spp. The growth of barley in a two-species mix with oat had materially reduced the intensity of fusarium ear blight (Fusarium spp.) and fusarium foot rot (Fusarium spp.). A three-species mix, in turn, had significantly reduced the development of Oculimacula spp., the causal agents of eyespot.