The results of a karyological study on the hazel dormouse Muscardinus avellanarius trapezius from Turkey were presented in this study. Using conventional staining and G- and C-banding techniques, 10 specimens were cytogenetically studied. The G- and C-banding patterns of Turkish specimens of this subspecies were provided for the first time in this study. The karyotype was composed of 2n = 46, NF = 90 and NFa = 86. A secondary constriction was visible in one pair of metacentrics (no. 9). All of the chromosomes possessed heterochromatic bands in the centromeric and pericentromeric regions. The X chromosome was a medium-sized metacentric and the heterochromatic region was restricted to the centromere. The Y chromosome was a very small acrocentric and possessed small centromeric block of heterochromatic.