The Pattern Informatics algorithm, which has recently shown promising performance for earthquake forecasting in Southern California, has been used to detect the locations where precursory seismic activity occurred preceding the 1999 Chi-Chi, Taiwan, earthquake. Using the Pattern Informatics method as presented in this paper, the epicenter of the Chi-Chi main shock was found to exhibit signatures of anomalous activity related to the seismic activation and quiescence in the Taiwan region over a time span of about 6 years before the main shock. A strategy of making intermediate-term earthquake hazard assessment by means of Pattern Informatics is therefore proposed on the basis of retrospective analysis of the Chi-Chi earthquake.