Pseudo-chaotic time hopping (PCTH) is a recently proposed modulation scheme for UWB impulse radio. PCTH exploits concepts from symbolic dynamics to generate aperiodic spreading sequences. In this paper, we present a general analytical expression for the average BER (bit-error-rate) of a synchronous multi-access PCTH system, as a function of the cross-correlation between the users' signatures in an AWGN (additive white Gaussian noise) channel. Also, it is shown that with enough users an error floor in the BER can develop.