Radio-frequency identification (RFID) is a growing technology, with the potential for reducing medical errors and improving the quality of healthcare in hospitals. The benefits include more secure and safe access in the healthcare environment (with the possibility, for example, to track patients, personnel, and equipment), as well as providing the means to easily identify patients and their medications with low risk of error. In this paper, we present an overview of the challenges faced in antenna design, electromagnetic modeling and wave propagation for RFID implants. The performance of ultra-high-frequency (UHF) subcutaneous tag antennas was investigated numerically and validated with measurements. Furthermore, the wave propagation between an off-body reader and an implanted tag was analyzed, in both free space and a scattered indoor environment. Results demonstrated that a passive tag solution allows a very limited communication range, due to the body losses, the electrically small size of the antenna, and nulls in the radiation pattern. In comparison, a maximum communication range of 10 m was predicted as achievable for an active tag operating indoors with a limited power (-20 dBm).