Mussau Island is the largest island of St Matthias Islands, Papua New Guinea, at 1°25′01″S 149°37′59″E / 1.417°S 149.633°E. It is currently part of the New Ireland Province of Papua New Guinea. The island is a noted Biodiversity hotspot with pristine primeval Rainforest covering most of Mussau's hilly landscape. The island has over 243 endemic plant species as well as at least 47 native butterfly species.