The karyological analysis of fifty-five voles collected in different localities of Greece showed that they belong to the following cytotypes ofMicrotus (Terricola) thomasi:«thomasi» 2n= 44; FN = 44, «atticus» 2n= 44; FN = 46, «subalpine» 2n= 42; FN = 42 and «Rb-subalpine» 2n= 40; FN = 42. A comparative study of the G-banding patterns among them showed that the first two, differing in a pericentric inversion, both represent the type speciesM. (T.) thomasi.Their distribution is intermingled and extends from central Greece to Peloponissos. The «subalpine» cytotypes distributed in mountainous central Greece, in Mt. South Pindos and in lowland of Ipiros, differ by a Robertsonian centric fusion. They display moreover a tandem fusion, a pericentric inversion and addition of heterochromatin which differentiate them to a greater extend from the type species and may consequently be consider to belong to another taxon of «thomasi» complex. The relatioships among these cytotypes is also descussed.