Well-functioning groups enforce social norms that restrain opportunism. We study how the assignment to the top or bottom of the caste system affects the altruistic punishment of norm violations. Individuals at the bottom of the hierarchy exhibit a much lower willingness to punish norm violations that hurt members of their own caste. We can rule out self-selection into castes and control for wealth, education and political experience. We thus plausibly identify the impact of caste status on altruistic punishment. The lower willingness to punish may impair the low castes’ ability to enforce contracts, to ensure property rights and sustain cooperation.