We present sulfur isotope ratio measurements of bone collagen from animals (n = 75) and humans (n = 120) from five sites dating to four chronological periods (Chalcolithic, Punic, Late Antiquity-Early Byzantine, and Islamic) from the Balearic Islands of Ibiza and Formentera, Spain. This study is a follow up to previously published δ13C and δ15N values by [Fuller et al.: Am J Phys Anthropol 143 (2010) 512–522] and focuses on using δ34S values to better understand the dietary patterns of these populations through time and to possibly identify immigrants to these islands. The range of δ34S values (10.5–17.8‰) observed for the animals was relatively broad, which suggests that a significant sea spray effect has added marine sulfates to the soils of Formentera and Ibiza. The mean δ34S values of the different human populations were found to be: Chalcolithic (16.5 ± 1.4‰), Punic rural (13.6 ± 1.7‰), Punic urban (12.9 ± 1.8‰), Late Antiquity-Early Byzantine (12.3 ± 2.1‰), and Islamic (9.1 ± 2.7‰). These human δ34S results are similar to the animal data, a finding that supports the notion that there was little marine protein consumption by these societies and that the diet was mainly based on terrestrial resources. During the Punic and Late Antiquity-Early Byzantine periods the δ34S values were used to identify individuals in the population who likely were not born or raised on the islands. In addition, 18 of the 20 individuals analyzed from the Islamic period have δ34S values that indicate that they were immigrants to Ibiza who died before acquiring the new local sulfur isotopic signature. Am J Phys Anthropol 2012. © 2012 Wiley Periodicals, Inc.