In this paper, we discuss the energy efficient multicast problem in ad hoc wireless networks. The problem of our concern is: given an ad hoc wireless network and a multicast request, to find a multicast tree such that the total energy cost of the multicast tree is minimized. Each node in the network is assumed to have a fixed level of transmission power. We first prove the problem is NP-hard, and then propose three heuristic algorithms, namely Steiner tree based heuristic, node-join-tree and tree-join-tree greedy algorithms. Extensive simulations have been conducted and the results have demonstrated the efficiency of the proposed algorithms.