Real estate prices can deviate from their fundamental value due to rigid supply, heterogeneity in quality, and various market imperfections, which have two contrasting effects on bank stability. Higher prices increase the value of collateral and net wealth of borrowers and thus reduce the likelihood of credit defaults. In contrast, persistent deviations from fundamentals may foster the adverse selection of increasingly risky creditors by banks seeking to expand their loan portfolios, which increases bank distress probabilities. We test these hypotheses using unique data on real estate markets and banks in Germany. House price deviations contribute to bank instability, but nominal house price developments do not. This finding corroborates the importance of deviations from the fundamental value of real estate, rather than just price levels or changes alone, when assessing bank stability. (C) 2009 Elsevier B.V. All rights reserved.