This book constitutes the reviewed proceedings of the 5th International Workshop on Algorithmic Aspects of Wireless Sensor Networks, ALGOSENSORS 2009, held in Rhodes, Greece, July 10-11, 2009. The 21 full papers and two brief announcements were carefully selected from 41 submissions. This workshops aimed at bringing together research contributions related to diverse algorithmic and complexity-theoretic aspects of wireless sensor networks. The topics include but are not limited to optimization problems, noise and probability, robots and tours.