Green toads from Sardinia are on average 30% longer and twice as heavy as those from the Italian Peninsula. The skeletochronological analysis of an island and a mainland population showed that differences of size were not a consequence of a longer lifespan of island toads, but of their higher growth rate in the pre-adult stages of life. The effects of these differences of size on the acoustic communication system of the species were analysed. Significant differences were observed in both spectral and temporal properties of the calls. The longer size of insular toads resulted in a reduction of 0.24 kHz of the fundamental frequency. Differences of temporal properties were mostly due to the different thermal conditions of calling males: with respect to mainland toads, island green toads were generally active at lower water temperatures and, at the same water temperature, they had proportionally lower body temperatures.