Brachycephalus hermogenesi is an endemic leaf litter inhabitant of the Atlantic forest of southeastern Brazil, whose original distribution included a restricted area near the boundaries of the States of São Paulo and Rio de Janeiro. We were surprised to find out, while conducting herpetofaunal surveys at Estação Biológica de Boracéia (EBB), that the background forest insect–like sound we have been searching for corresponded to calling individuals of the species. Males call during the day at high densities, hidden under the leaf litter. Individuals do not answer playback, seem to move very infrequently, and seem to ignore nearby calling activity. We gathered data on annual and daily vocal activity of the species at EBB, observing a total of 1,549 calls given by 31 focal individuals in November 2003 and 2005. The call varies from short single note calls to calls composed of groups of two to seven similar notes emitted at regular intervals. We also extend the known distribution of the species southward to the State of São Paulo.