Whatever the source or explanation of bias in forecasts of company earnings, if such bias persists, it is potentially discoverable and exploitable by investors. This research addresses (1) whether characterizing forecasts as if they were a homogeneous group with respect to bias is accurate or useful and (2) whether a long-term record of forecast errors contains information useful in predicting subsequent errors. We found that earnings forecasts are heterogeneous with respect to direction and degree of bias. We also found evidence of extremes in optimism and pessimism and that extreme errors tend to persist in the same direction, which suggests certain potentially profitable trading strategies.