Companies listed on China's Shenzhen Stock Exchange Small and Medium Enterprise Board are required to release preliminary performance reports before the end of February if they cannot file annual reports by that time. Although this mandate might improve the timeliness of information, we find that such preliminary releases are inaccurate and optimistic, potentially misleading investors. Sixteen percent of preliminary reports contain significant inaccuracies (i.e., when actual numbers deviate from preliminary ones by at least 10 percent). Firms in earlier stages of the auditing process, as well as those with low-quality preliminary reports in prior years, poorer performance, greater accounting complexity, and fewer resources, are more likely to issue low-quality preliminary performance reports. Market reaction tests indicate that investors consider preliminary releases to be informative and generally cannot differentiate between high-quality and low-quality preliminary releases. Moreover, when annual reports are filed, investors are surprised by the differences between the annual reports and the preliminary reports. Thus, our paper demonstrates that mandatory disclosure requirements may have unintended negative consequences.