Introduction Many legislatures are not well apportioned, with some constituencies having a larger or smaller share of seats than would be dictated by the relative sizes of their populations. According to the mainstream literature on legislative bargaining, malapportionment should lead to the formulation of biased policies that mirror the overrepresentation or underrepresentation of different constituencies. However, these same biases could also be generated by other economic and institutional factors. This paper explores the question as to whether certain policy biases are actually caused by legislative malapportionment or are the outcome of a more structural type of political equilibrium. In particular, we exploit three natural experiments that occurred in Argentina in order to estimate the extent of the effects of legislative malapportionment on the Argentine federal tax sharing scheme.