Understanding the reproductive characteristics of Sabellastarte spectabilis (Grube, 1878), an economically important polychaete worm collected for the aquarium trade, is essential to the development of artificial propagation and conservation of coral reefs. The purpose of this study was to determine whether S. spectabilis is hermaphroditic. Using histological techniques, 180 individuals were examined for gametes. Gametes were present only in abdominal segments. Primary oocytes were 7–8 μm in diameter in histologically prepared sections. Sperm appeared as round black dots about 2 μm in diameter on histologically prepared slides. Most individuals sampled had only one type of gamete in the coelom, but both eggs and sperm were seen in the coelom of 15% of individuals, demonstrating the occurrence of hermaphroditism in Hawaiian populations of S. spectabilis. The sex ratio of males to females was skewed significantly toward males in both the small (6–8 mm diameter) and medium (9–10 mm diameter) sized worms. Among the largest worms (11–13 mm diameter), the sex ratio did not diverge significantly from 1 :1. There was a significantly higher proportion of hermaphrodites (30%) in the large size class. Worms of unknown gender, although present in all size classes examined, were most frequent (33%) in the medium size class. These patterns are consistent with sequential (protandrous) hermaphroditism.