I describe a new species of treefrog of the genus Litoria from Sudest Island, in the Louisiade Islands, off the southeastern tip of New Guinea. The new species is readily distinguishable from all other Papuan species of the genus except L. prora and L. humboldtorum in its possession of fully webbed hands and a fleshy rostral spike. It is distinguished from these species by its larger size, reduced crenelated fringes on arms and legs, absence of heel lappets, reduced papillae on the mandibular margin, and details of color pattern. I describe the tadpole for the new species and show that it differs from that of L. humboldtorum in morphology and color pattern. All three species form cohesive, distinct clusters in multivariate morphometric space. Morphologically, the new species most closely resembles L. humboldtorum, known from Yapen Island and the nearby New Guinea mainland 2000 km to the northwest. The new species was not found in recent surveys of nearby Rossel and Misima islands, the other large islands of the Louisiade group, and it may be restricted to Sudest Island.