The small, green sea hare, Phyllaplysia viridis, originally described from Indonesia in 1905, has rarely been recorded since. Because the taxonomic status of Phyllaplysia is uncertain, there remains a need for clarification of the currently accepted species. To do so, we used contemporary specimens from eastern Australia and Indonesia to redescribe P. viridis using photographs and scanning electron imagery of its external and internal morphology. Although all examined specimens were small, consistently green animals, images revealed some variation in colour and pattern among adults. Molecular data confirmed the presence of P. viridis in the Philippines, Indonesia and eastern Australia. A phylogenetic tree based on available COI barcode sequences illustrate a sister relationship with other Phyllaplysia. The construction of a haplotype network failed to show any marked geographic structure among specimens.