Deformed wing virus (DWV) is one of the most widespread viruses that infect honey bee colonies. The route of infection is directly through contaminated food, feces, and air, or indirectly through the varroa mite, which acts as a vector. Positive DWV samples were obtained from Carniolan honey bee (Apis mellifera carnica) colonies and of varroa mites from the whole territory of Slovenia during a survey between 2007 and 2014. Nucleotide sequences of 471 nucleotides for the L protein gene and 573 nucleotides for the helicase gene were compared. High genetic diversity was observed among these Slovenian Carniolan honey bee DWV field samples, as well as with almost all the strains previously found in other countries in Europe. Phylogenetic analyses in two regions of the viral genome show that several of the DWV strains obtained from honey bees and varroa are genetically very closely related, confirming the important role of varroa in the transmission of DWV. Identification of closely related sequences also confirmed that the same strains of DWV have been successfully transmitted between various honey bee colonies and apiaries. It has also been established that simultaneous infection, in one apiary, of honey bees with two or more different strains of DWV is quite frequent. This is phylogenetic study that compares honey bee and varroa DWV strains from Carniolan honeybees.