The nature of the sexual system (protandry, gonochory) and the frequency of female spawning (semelparous, iteroparous annual, iteroparous biennial) in the crangonid Sclerocrangon boreas remain uncertain. We addressed these questions by examining population sex ratio, anatomy and histology, and gonad and oöcyte sizes. Gonochory is supported by several facts: sex ratio was balanced at the smallest shrimp sizes, no intermediate sex form was found, and there was no evidence of degeneration of male gonad at the sizes where this might have been expected to occur. A majority of larger females, if not all, had a structure linking the ovary to the base of the fifth pereiopod but the presence of this structure on small females suggests it is not a degenerate vas deferens. Iteroparity is supported by the presence of two generations of oöcytes in females, including those gravid, and female biennial spawning is supported by the small size of ovaries/oöcytes in gravid females.