An energy-efficient dual-band transceiver for unified body sensor network is presented. The transceiver provides 30-70 MHz body channel communication (BCC) and 402-405 MHz medical implant communication service (MICS). For low energy consumption, the BCC and MICS band circuits in the receiver operate concurrently with their front-ends shared. As a result, up to 30% energy saving is achieved. The dual-band front-end circuits consist of a cascaded LC tank LNA and a current-recycling concurrent-down conversion mixer. The proposed LNA provides 16 dB gains both in the BCC and MICS bands and suppresses interferences coupled through the human body by more than 10 dB. For BCC robustness, a variable adaptive frequency hopping is applied. The transceiver fabricated with 0.18 mu m CMOS is fully compatible with the FCC regulations for MICS and consumes 10.8 mW and 4.9 mW in its RX and TX modes, respectively. The adjacent channel rejections are measured at > 30 dB in the dual-bands.