Population genetic studies have shown that the Bosnian-Herzegovinian (B&H) population is a part of the European gene pool, but there has been limited information on the genetic structure of ancient B&H populations. This study aimed to determine the frequency and distribution of mitochondrial DNA (mtDNA) haplogroups for a medieval Bosnian population. Thirty-four samples, excavated from medieval necropolises located within the borders of medieval Bosnia, were analyzed. Sequencing of the mtDNA hypervariable segment 1 (HVS1) region and RFLP analysis were performed for haplogroup determination. All 32 samples were identified as haplogroup H, with subhaplogroups H2a and H5 in 30 and 2 samples, respectively. The frequency of the H haplogroup was significantly different between the studied samples and previous studies of contemporary B&H populations, where the H haplogroup frequency was approximately half that of the ancient population studied here. A significant difference in H haplogroup frequency compared with other medieval populations outside of Bosnia was also observed: the ancient B&H population is most similar to ancient Italians. These results provide insight into the mitochondrial landscape of populations that inhabited the territory of present-day Bosnia and Herzegovina in the Middle Ages. Our study reveals that inhabitants of medieval Bosnia carried genetic lineages that exist today in B&H populations, suggesting continuity of mtDNA haplogroups over a long period of time, regardless of various historical demographic events that shaped the genetic structure of the modern B&H population.