Evaluation of size discount and control premium in mergers and acquisition of companies in Brazil. The types and magnitudes of premiums and discounts on business valuations are often the cause for the differences between the values found by the parties involved in a negotiation. Main discounts are due to the purchase of minority interest, the size and illiquidity of the company. Empirical evidence indicates that these discounts are substantial, usually far greater than people realize until they have access to the market data. This paper tries to assess whether the effect size and effect control in the business of mergers and acquisitions (F&A) of publicly traded companies in Brazil, using as a parameter the price-earnings index (P/E) of transactions. The sample used in this survey had 91 transactions in F&A in the period from January 1997 to July 2008. This work revealed that the discount size in Brazil, around 44% is in line with studies conducted in Argentina, in the order of 50%. However, the discount size was found to be more than double that reported by the same author in the U.S., in the order of 20%. In the case of the effect of control, the premium found was approximately 187%, much higher than reported in studies in the U.S. (about 32%) or that found in empirical study in Argentina (39%), revealing the high value assigned to the controlling shareholder in publicly traded companies in Brazil