Optical Wireless Links as an alternative to Radio-Frequency for Medical Body Area Network It is now established that Optical Wireless Communications (OWC) technology is a promising alternative or a complement one to radio-frequencies for indoor transmissions. Considering that using OWC permits reducing electromagnetic pollution in human environment, this technology can be also a good candidate for Wireless Body Area Networks (WBAN) in particular for medical applications such as health monitoring. In this paper we investigate the use of on-body OWC for mobile medical WBAN. Based on transmission scheme exploiting diffuse optical reflections over the patient environment, we investigate a star BAN topology using spreading codes for multiple access. We have developed a theoretical analysis to determine the performance of such network considering that the patient is moving in the room. The achievable quality of service for a typical health monitoring application is reported and discussed regarding the performance required by medical applications.