Over the last few years, there has been an emerging interest in applying ultrawideband (UWB) communications in wireless sensor networks, mainly due to the low-complexity and low-power consumption of UWB technology. In particular, low-complexity receiver like the energy detection (ED) receiver is a potential candidate for sensor network applications. However, the presence of network interference will severely degrade the performance of such receivers. In this paper, we analyze the bit error probability performance of the ED receiver in the presence of uncoordinated UWB interference. We model the network interference as an aggregate UWB interference, generated by elements of uncoordinated UWB networks scattered according to a spatial Poisson process. Our analytical framework allows a tractable performance analysis and gives sufficient insight into the effect of uncoordinated network interference on UWB systems.