An adaptive parallel interference cancelation (APIC) scheme is proposed for the multicarrier direct sequence code division multiple access (MC-DS-CDMA) system. Frequency diversity inherent in the MC system is exploited through maximal ratio combining, and an adaptive least mean square algorithm is used to estimate the multiple access interference. Theoretical analysis on the bit-error rate (BER) of the APIC receiver is presented. Under a unified signal model, the conventional PIC (CPIC) is shown to be a special case of the APIC. Hence the BER derivation for the APIC is also applicable to the CPIC. The performance and the accuracy of the theoretical results are examined via simulations under different design parameters, which show that the APIC outperforms the CPIC receiver provided that the adaptive parameters are properly selected.