The problem of finding a minimum diameter spanning tree (MDST) of a set of n points in the Euclidean space is considered. The diameter of a spanning tree is the maximum distance between any two points in the tree. A characterization of an MDST is given and a -time algorithm for solving the problem is presented. The authors also show that for a weighted undirected graph, the problem of determining if a spanning tree with total weight and diameter upper bounded, respectively, by two given parameters C and D exists is NP-complete. The geometric Steiner minimum diameter spanning tree problem, in which new points are allowed to be part of the spanning tree, is shown to be solvable in time.