This paper presents a theoretical performance analysis of frequency hopped multiple-access communication systems with spectrally overlapping hopping channels. Taking into account cochannel as well as the adjacent-channel interference, we develop an accurate interference analysis for the noncoherent detection of a FH/BFSK signal in the presence of other interfering signals. A new closed form expression for the corresponding bit error rate is derived in an AWGN Rayleigh faded channel. This result provides an accurate design approach for the selection of the channel spacing in frequency hopping multiple-access systems It is shown that the spectral efficiency depends on the form of the waveshaping pulses and the separation between adjacent hopping channels. When compared with the performance of systems with nonoverlapping channels, numerical results suggest that an improvement of about 100% is possible.