How widespread is tax evasion – and what does that imply for the true extent of inequality? This research explores these questions by analyzing a unique dataset of leaked customer lists from offshore financial institutions matched to administrative wealth records in Scandinavia. The results show that offshore tax evasion is highly concentrated among the rich. The top 0.01% of households by wealth evade about a quarter of the taxes they owe, largely by concealing assets and investment income abroad. Top wealth shares in Denmark, Norway and Sweden increase substantially when adding back these unreported assets, highlighting the need to take account of tax evasion to measure inequality accurately.