The pierid Charonias theano (Boisduval), an endangered butterfly species, has been rarely observed in nature, and has not been recorded in the state of São Paulo in the last 50 years despite numerous efforts to locate extant colonies. Based on museum specimens and personal information, C. theano was known from 26 sites in southeastern and southern Brazil. Recently, an apparently viable population was recorded in a new locality, at Serra do Japi, Jundiaí, São Paulo, with several individuals observed during two weeks in April, 2011. The existence of this population at Serra do Japi is an important finding, since this site represents one of the few large forested protected areas where the species could potentially persist not only in the state of São Paulo, but within its entire historical distribution.