The Brazilian stock market shows strong mean reversion, with greater intensity for returns with a lag from 3 to 27 months. The evidences found suggest that about 50% of future prices formation, to these intervals, can be explained upon their past prices. This percentage stays between 30 and 50% for lags from 6 to 24 months. For 1 month intervals, it was not found significant reversion and, for 30 months, it starts loosing strength, which suggests a U shaped reversion pattern trough the time. It means that it starts null, increases, keeps itself significant, reaches a maximum figure and decreases gradually until loosing its significance. Being the mean reversion a not random walk modality, the random walk hypothesis is rejected.