The asymmetrical aksak rhythm represents one of the distinctive and most vital features of the musical traditions on the Balkans. In spite of that, this rhythm system - discovered only at the beginning of the 20th century in Bulgaria - has almost been unknown, both to the musicological/ ethnomusicological sciences, and to the world of serious music. Owing to inadequate transcriptions of most of the musical notations of the vocal and instrumental music from the beginning of the 20th century, it was hardly possible to perceive the presence of this asymmetric rhythm in the Balkan area. Because of that the ethnomusicological results of this paper are based primarily on the transcribed musical-folkloristic material dating from the second half of the 20th century. But, regardless of that or other difficulties, the musical material available enabled me to establish the presence and the different forms of the aksak rhythm in the Balkan region. Along this guideline, my intention is, on the basis of the available literatures and musical notations, to point out the most frequent forms and the distribution of the aksak rhythm, its earliest appearances in the works of composed music, as well as the continuity and changes of this rhythm in the vocal and instrumental tradition of the Balkan peoples.