Look for a set of three leaflets on every stem. Poison ivy occasionally grows with five or seven leaflets on a stem, but the group of three is most common.
Observe the leaflets themselves. A poison ivy leaflet is usually 4 inches long or smaller. Its shape is oval and it may be toothed. The leaflets are bright green during spring or summer and turn yellow or bright red in the fall. They may look waxy or shiny.
Check the plant's growth habit. Poison ivy usually grows as a vine that twines up a tree or a building. In this form, its stem is thick and woody and displays aerial roots. Sometimes, poison ivy grows as a small shrub with thin stems. In this form it remains under 3 feet in height.
Look for flowers in the springtime and berries in the fall. Small, white poison ivy flowers hang together in loose clusters. The berries are also white and hang in bunches.