We analyze the performance of direct-sequence spread spectrum multiple access (DS/SSMA) systems, which use trellis coding with asymmetric phase shift keying (PSK) modulation. By designing the signal constellation to be asymmetric, we obtain a performance gain for the DS/SSMA system over the systems using the traditional symmetric signal constellation. Bit error probability analysis of the proposed system is carried out for some cases. Examples are given to show the performance gain due to the asymmetry of the signal constellation. (C) 1998 Elsevier Science B.V. All rights reserved.