Geographical variability in birdsong is in constant interest of research projects already for decades, as it has a potential to clarify numerous aspects of bird ecology and evolution. For Oscines, whose song is learned, geographical variability of song may reflect cultural and sometimes even genetic differences among populations. The phenomenon of geographic variability in song is apparently common, as it has been proven in many species with various complexity of their vocalization. In the present study, we focused on the River Warbler (Locustella fluviatilis). This species is extraordinary among Oscines, as its´ song is extremely simple. Our aim was to find out whether even such simple song differ between four geographically distant populations (minimum distance was 95 km, maximum 370 km). We recorded a total of 63 individuals (on average 15 individuals per site). Three recording sites were situated along the whole east-west gradient of Slovakia (Senné, Poiplie, Devínske Jazero) and the fourth one in Moravia (around Uherské Hradiště). We measured 6 frequency and temporal parameters in the song of each individual. Discriminant analyses showed three of these parameters to be significantly variable among the studied populations. The success in assignment of individuals into the origin population was only 57 %. However, there was an obvious trend for differentiation between the populations located on the east (Senné, Poiplie) and on the west (Devínske Jazero, Uherské Hradiště). Thus, although we confirm that the song of the River Warbler is geographically variable, the measured parameters do not reliably differentiate the local populations. Probably, other characteristics would increase the success of discrimination, but considering the simplicity of the River Warblers´ song, it seems likely that the observable differences are rather on regional than local level.