The dissertation is an analysis of the market risk that an investor faces in a passive management stock fund linked to the IBOVESPA, supposing that the Brazilian financial market is subject to financial instabilities, which in theory can make the returns to become distant from a normal distribution. The risk is measured through the VaR and ETL, the latter being accepted as a coherent risk measure. The ETL is estimated through the VaR, which in turn is estimated by two different methodologies: jump- diffusion process and the supposition of normal distributed returns. Through the methodology of jump- diffusion, the market risk can be measured when the returns distribution has fatter tails than the normal distribution, as well as assimetry.