In controlled laboratory experiments with and without overlapping generations, we study the role of intergenerational altruism in public debt accumulation. Public debt is chosen by popular vote, pays for public goods, and is repaid with general taxes. We use an optimal control model to derive a theoretical benchmark. With a single generation, public debt is accumulated prudently. With multiple and over-lapping generations, the burden of debt and the risk of over-indebtedness are shifted to future generations. We find a weak but significant sign of intergenerational altruism, observing that the revealed debt preferences increase as the number of following generations decreases. However, we find considerably fewer intergenerational fairness concerns than one would expect on the basis of the behavioral and experimental literature. Instead, political debt cycles that vary with voters' age emerge. Debt ceiling mechanisms fail to encourage intergenerational altruism and do not mitigate the problem of burden shifting.