The aim of this study is to show how clusteranalysis can shed light on very complexvariation in a transitional dialect zone ineastern Finland. In the course of history thisarea has been on the border between Sweden andRussia and the population has clearly been oftwo kinds: the Savo people and the Karelians.It is a well-known fact that there is variationamong these dialects, but the spread and extentof the variation has not been demonstrated previously.The idiolects of the area were studied in thelight of ten phonological and morphologicalfeatures. The material consisted of recordingsof 198 idiolects, totalling around 195 hoursand representing 19 parishes. The variation wasanalysed using hierarchical cluster analysis.While the analysis showed the extent of thevariation between idiolects and parishes, italso demonstrated how the effects of the oldparishes, borders and settlements are stillvisible in the dialects. On the parish level,the data formed clear clusters that correspondwith the main dialects in the area and itssurroundings. On the idiolect level, however,the speakers from the surrounding areas formedfairly homogenous clusters but the idiolectsfrom the Savonlinna area were spread acrossalmost all clusters.