Most existing routing protocols for mobile ad hoc networks (MANETs) use a single routing strategy for different types of networks. Routing protocols suitable for small networks may not scale well in large networks. Routing protocols that perform well in sparse networks may not be suitable for dense networks. To achieve good performance, different routing strategies should be used for different types of networks. This philosophy motivates our design of a new routing protocol called the adaptive cell relay (ACR) routing protocol. Our ACR protocol can adapt the routing strategy for networks with different node density so high efficiency, low delay, and scalability can be achieved. Extensive simulation results demonstrate that the ACR has much better performance and scalability than a popular routing protocol-location-aid routing (LAR). In addition, both the analysis and the simulations show that the ACR routing protocol incurs only about 25% of the routing overhead of the LAR routing protocol.