With the purpose of explaining professional audit costs in Swedish municipalities, we hypothesised that audit costs are partly driven by various signalling and monitoring incentives in order to manage stakeholder relationships. Our model of the determinants of audit costs was tested on data from Swedish municipalities, thus extending the study of audit costs to political organisations in a Scandinavian institutional context. The test supported to some extent the traditional propositions of organisational complexity, risk and market determinants, as well as the proposition of the political environment. Our results indicate that audit costs are used to signal accountability, thereby suggesting that audit as a signal could be managed without managing professional auditors.