S’arrepentina is a genre of extemporary poetry performed by semi-professional poets, both at informal gatherings and in public contests in south-central Sardinia. The name arrepentina refers both to the genre/performance in its entirety, and to the set of metrical forms and rhyme schemes used during the performance. Lines occur in non-strophic (stichic) form, and are made up of halflines linked by a complex system of rhymes. Unlike similar metrical forms, s’arrepentina is not performed in a “free rhythm” singing style. Typically, poets improvise their verses accompanied by an accordion, which provides a steady pulse. In this study, we investigate variation in nine arrepentinas and we aim to determine the degree of rhythmical variability in each halfline by measuring it against the underlying meter provided by the musical accompaniment. From the analysis, it emerges that the rhythmical variants are concentrated at specific positions, and their distribution suggests an asymmetry between the two halflines. Some inter-individual variation among the poets also appears in their preference for one type of variant over others.