In this paper, we investigate the performance of an adaptive full parallel interference cancellation (FPIC) multiuser detection scheme based on the least mean square (LMS) algorithm for direct-sequence code-division multiple-access (DS-CDMA) communication systems. Simulation results show that the proposed FPIC multiuser detector outperforms the NLMS-based partial PIC (NLMS-PPIC) scheme over flat fading channels under imperfect channel estimation. Moreover, over a two-path frequency selective fading channel, the proposed adaptive FPIC detector is superior to the NLMS-PPIC and shows the effective cancellation of the multiple access interference (MAI) even with moderate channel estimation errors.