I describe a new treefrog of the Litoria gracilenta group from the lowlands along an outlying volcanic peak in southeastern Papua New Guinea. The new species is distinctive among members of that group in a combination of details of color pattern and morphometric characters, and it is further unique within that group in being the only species known to have a call consisting of several notes. It is also unusual for the group in having been found breeding in a stream. This species complex has an extensive but disjunct range spanning the entire extent of New Guinea, outlying islands to the west and the east, and eastern Australia. The new species fills in a range gap of 830 km between its nearest relatives to the northwest and southeast.