This paper investigates a relatively new file structure known as an ordered hash table which combines the flexibility of indexed sequential files with the rapid access of traditional hashing methods. The main results of the paper are: (1) a characterization of optimal hash tables allowing for differing access frequencies among the keys, and (2) an algorithm to construct an optimal ordered hash table. The details of the algorithm are given for the special case of unit bucket size but it may be extended to cover large bucket sizes.