Verticillium albo-atrum causes unprecedented wilt and mortality of the invasive tree-of-heaven (Ailanthus altissima) within forests of south-central Pennsylvania. Stem inoculation of potted Ailanthus seedlings in the greenhouse and canopy Ailanthus trees in the field with V. albo-atrum resulted in 100% mortality. Stem inoculation of understory striped maple saplings in the field also resulted in 100% mortality. However, the high susceptibility of striped maple was not observed in naturally infected stands, where only 1% of striped maple saplings exhibited Verticillium wilt. Inoculation of chestnut oak, northern red oak, red maple, sugar maple, white ash, and yellow-poplar seedlings or canopy trees with V. albo-atrum did not induce wilt symptoms. Non-Ailanthus tree species growing adjacent to dead and dying Ailanthus trees in the field were asymptomatic. Pending further studies, V. albo-atrum should be considered as a potential biocontrol agent for invasive Ailanthus.