National and international regulatory agencies by issuing new standards have tried to bring the accounting recorded values near to economic values. Nevertheless, it is understood that the latter carry a deeper level of subjectivity, on the grounds that completely new values will be obtained by the adoption of different conditions. This study aims to perform a comparative analysis between two company valuation methods: the Discounted Cash Flow and the Residual Income Valuation while performing the impairment test. The study case uses the database prepared by a telecommunications company to its subsidiary in the Internet sector for the purpose of the impairment test assessment. Some points have been identified as deserving special attention in a company’s valuation assessment, namely the discount rate and the growth rate.  The results show that: 1) a firm’s economic value is sensitive to the use of a sole growth rate to calculate the perpetuity, considering that any changes in the rate will alter the decision based on the test; 2) the setup of a discount rate as a parameter in a firm’s valuation assessment is a fundamental point for the write-off decision resulting from an impairment test.