Two traditional methods of managing equity portfolios are investing based on price momentum and value-based contrarian investing. These strategies may be motivated by a behavioral theory of under- and overreaction to news or by empirical research, mostly for the NYSE, that has found persistence in price movements over short horizons and reversion to the mean over longer horizons. However, the apparent success of these strategies may be due to institutional factors and the mismeasurement of risk, or it may result from data mining. For these reasons, we studied all major German companies listed on the Frankfurt Stock Exchange for the three decades between 1961 and 1991. The dynamics of stock prices in Frankfurt are remarkably similar to New York. The data suggest that equity prices reflect investor forecasts of company profits that are predictably wrong.