Anthropologists have provided rich field descriptions of the norms and conventions governing behavior and interactions in small-scale societies. Here, we add a further dimension to this work by presenting hypothetical moral dilemmas involving harm, to a small-scale, agrarian Mayan population, with the specific goal of exploring the hypothesis that certain moral principles apply universally. We presented Mayan participants with moral dilemmas translated into their native language, Tseltal. Paralleling several studies carried out with educated subjects living in large-scale, developed nations, the Mayan participants judged harms caused as the means to a greater good as more forbidden than harms caused as a side-effect (i.e., "side-effect bias"). However, unlike these other populations living in large-scale societies, as well as a more educated and less rural Mayan comparison group, the target rural Mayan participants did not judge actions causing harm as worse than omissions (i.e., "omission bias"). A series of probes targeting the action-omission distinction suggest that the absence of an omission bias among the rural Mayan participants was not due to difficulties comprehending the dilemmas, using the judgment scale, or in attributing a greater causal role for actions over omissions. Thus, while the moral distinction between means and side-effect may be more universal, the moral distinction between actions and omission appears to be open to greater cross-cultural variation. We discuss these results in light of issues concerning the role of biological constraints and cultural variation in moral decision-making, as well as the limitations of such experimental, cross-cultural research. (Contains 2 tables and 1 figure.)