This study aims to investigate whether the persistence of earnings, accruals and cash flows are influenced by the difference between accounting and taxable income (book-tax differences; BTD). This investigation helps in two research lines. First we have expanded the literature that interprets the BTD. We used the discretionary part of the BTD to estimate managerial manipulation. Our contribution is to use a different method to estimate the BTD through the residual of a multiple regression. Secondly, we attempted to investigate whether discretionary BTD appear to serve as a useful signal of earnings persistence. We test the model with a sample of 21 listed Tunisian firms in the period from 2003 to 2012. The results illustrate the importance of BTD in indicating the persistence of earnings and accruals.