An adult long-distance swimmer attempting to cross the ‘Alenuihāhā Channel between the Hawaiian islands of Hawai'i and Maui was twice bitten by a cookiecutter shark (Squaliformes, Dalatiidae, Isistius sp.). One of these bites presented as an open, round, concave wound typically observed in cookiecutter shark bites inflicted by members of this genus on a broad spectrum of large biota such as marine mammals, elasmobranchs, and bony fishes. The open wound was debrided, subjected to negative pressure wound therapy, and a split thickness skin graft harvested from the left thigh. Postoperative recovery was complicated by delayed healing of the inferior portion of the graft, and cultures and biopsy were normal skin flora and normal tissue, respectively. At 6 months after the incident, the area appeared to be healing with a stable eschar, and by 9 months the wound was healed. Humans entering pelagic waters at twilight and nighttime hours in areas of Isistius sp. occurrence should do so knowing that cookiecutter sharks are a potential danger, particularly during periods of strong moonlight, in areas of man-made illumination, or in the presence of bioluminescent organisms.