Companies' cash flows have been subject of research all over the world, focusing on their predictive role. In Brazil, the law 11.638/2007, which determines the release of Cash Flow Statement allows broader studies in this field. This study investigates the effects of net earnings in helping to predict operational cash flows of open capital companies in Brazil. This research is bibliographical, documental, and predominantly quantitative through econometrical methods. The database ECONOMÁTICA was used to collect secondary data, and 326 non-finance open companies that participate in BM & FBOVESPA stock market were object of analysis during 24 quarters from 2007 to 2012, in a total of 4.217 demonstrations. The results demonstrate that net income lagged explains the Future Operating Cash Flow at 66.80%. Moreover, the conclusions show a significant difference in the prediction of operational cash flow from sector to sector. Finally, the conclusions show that the cash flow statement has an important role in reducing the levels of informational asymmetry, and that accountancy is significant in providing businessmen with useful and reliable information, helping them in the process of decision making.