Abstract: Hashing with lazy deletion is a simple method for maintaining a dynamic dictionary: items are inserted and sought as usual in a separate-chaining hash table; however, items that no longer need to be in the data structure remain until a later insertion operation stumbles on them and removes them from the table. Because hashing with lazy deletion does not delete items as soon as possible, it keeps more items in the dictionary than methods that use more careful deletion strategies. On the other hand, its space overhead is much smaller than those more careful methods, so if the number of extra items is not too large, hashing with lazy deletion can be a practical algorithm when space is scarce. In this paper, we analyze the expected amount of excess space used by hashing with lazy deletion.