This paper is concerned with orthogonal frequency-division multiplexing interleave-division multiple-access (OFDM-IDMA) systems over frequency-selective fading channels. Deliberate clipping is applied to reduce the peak-to-average power ratio (PAPR) of each user's transmitted signal. An iterative multiuser detection (MUD) technique is developed to recover the performance loss due to clipping. A semi-analytical signal-to- noise ratio (SNR) evolution technique is proposed, which can provide quick and accurate prediction of the iterative MUD performance. Numerical results show that the performance of OFDM-IDMA is not sensitive to the frequency selectivity of channels, and OFDM-IDMA is more power-efficient than other alternative multi-carrier transmission techniques. © 2008 IEEE.