© 2018 IEEE.Inter-network interference in ultra-wideband (UWB) wireless body area networks (WBANs) is analyzed using stochastic geometry with the objective of quantifying the inherent interference tolerance of UWB WBANs in terms of the bit error probability. Such networks are expected to be common in the IoT segment of 5G networks and our methodology may be extended to other network configurations. Our results show that the amount of interference that can be tolerated depends on the node density of a Poisson point process and the transmission power. Moreover, decreasing the number of pulses per burst while transmitting a bit may increase the interference tolerance. On the other hand, UWB WBANs cannot tolerate significant amounts of interference in networks of ultra-densely deployed nodes. In these situations, there will be a significant amount of inter-network interference, and it is essential to adjust the power levels of all the nodes. With this objective, the transmission power of all nodes is decreased and their levels are determined by using a game theoretical approach; specifically with a non-cooperative continuous-kernel game. These optimized power levels not only reduce interference but also enhance the energy efficiency, which is of critical importance for WBANs.