We confirm the results of prior studies that auditor tenure improves earnings quality on average. We extend their findings to show that the improvement in earnings quality resulting from longer auditor tenure is greater for firms with higher information asymmetry, after controlling for auditor’s industry specialization. We argue that audits of client firms with higher information asymmetry demand more client specific knowledge that cannot be gleaned from industry or general experience. Longer tenure helps auditors acquire such knowledge and therefore, the benefit of longer audit tenure is greater in firms with greater information asymmetry. We use bid-ask spread, return volatility, intensity of R&D expenditure and a composite distance measure to measure information asymmetry. Our results imply that frequent auditor changes are costlier for firms with higher information asymmetry. At the policy level, our results imply that mandatory auditor rotation is more (less) costly for firms with high (low) information asymmetry.