In this study, we present a small-size dual medical implant communications service (MICS) (402-405 MHz) and industrial, scientific, and medical (ISM) (2.4-2.48 GHz) band implantable antenna for continuous glucose-monitoring applications. The antenna is optimized for dual-band operation by combining an in-house finite-element boundary integral electromagnetic simulation code and particle swarm optimization algorithm. In order to test the designed antenna in vitro, gels mimicking the electrical properties of human skin are also developed. The optimized antenna is fabricated and measured in the gel. The simulated and measured bandwidths are found to be 20.4% MICS, 4.2% ISM, and 35.3% MICS, and 7.1% ISM, respectively. Although we have emphasized continuous glucose monitoring throughout this paper, the antenna and skin mimicking gels presented here can be used for many other wireless telemetry applications.