Ditto Pokémon can be encountered and caught while walking in the Wetlands area during morning and day times (level 17) and any time of day (level 41). Catching a higher-level Ditto will also require 15 water objects to be laid out in the Wetlands area. However, once the items are places there is no waiting period before it appears.
In the HeartGold and SoulSilver versions, the Safari Zone has moved from Fuschia City to the west of Cianwood. The player will only be allowed to bring objects into the Safari Zone after they complete the task of bringing a Sandshrew to the Safari Zone Game Warden. In HeartGold, Ditto also appears on Routes 35 and 47, as well as in the Cerulean Cave area.