We study whether regulators should reveal stress test results that contain imperfect information about banks' financial health. Although disclosure restores market confidence in banks, it misclassifies some healthy banks as risky. This encourages banks to choose portfolios deemed safe by regulators, leading to model monoculture and making the financial system less diversified. Under the ex-ante optimal disclosure policy, the regulator addresses this tradeoff by fully revealing stress test results when adverse selection is very severe or very mild, but never disclosing the results otherwise.