Most of the data collected by sensors are useful only when they are associated with position information. This paper proposes a simple and yet efficient location discovery algorithm, called Hop-Count Based Positioning (HBP), in ad hoc sensor networks. HBP allows each node to estimate its position more accurately even if only a small fraction of nodes (called landmarks) are equipped with GSP receivers, and therefore, the cost of network will be reduced considerably. HBP lowers the power consumption at each node by reducing the total packet transmission. To achieve the minimum packet transmission HBP allows only landmarks to produce and broadcast the position information packets, and uses unicast over broadcast whenever possible. HBP achieves more accurate position estimation by observing the different cases of hop sizes.