In this paper, we combine sectorized transmission with artificial noise to establish secrecy in decentralized wireless networks. The locations of the legitimate nodes and the eavesdroppers are both modeled by homogeneous Poisson point processes. Using sectorized antennas, each legitimate transmitter sends an information signal in the sector which contains its intended receiver, while simultaneously emitting artificial noise in other sectors, in order to provide secrecy against the eavesdroppers. We first separately characterize the reliability performance of the legitimate link and the secrecy performance against malicious eavesdropping. Then, we derive the secrecy transmission capacity to measure the networkwide secrecy throughput. To facilitate the practical system design, we provide a sufficient condition, in terms of the system parameters and constraints, under which a positive secrecy transmission capacity is achievable. The optimal transmit power allocation between the information signal and the artificial noise for achieving the maximal secrecy transmission capacity is also investigated. Our analysis indicates that sectorized transmission provides significant secrecy enhancements in decentralized wireless networks. © 2013 IEEE.