In signal equalization, a technique that allows reduction of the number of states of the Viterbi detector is the Delayed Decision Feedback !hquence Detector (DDFSD). In order to achieve good performance, it is esseptial to operate, before the DDFSD, an appropriate pdtering of the received sequence. This paper is devoted to performance evaluation of the DDFSD when the feedforward filter of a minimum mean square error d e cision feedback equalizer is adopted as a prefilter. A truncated version of the union bound is used to approximate the bit error rate. The analysis includes a method for determiuiug the error events that dominate the bound.