A bottlenose dolphin, Tursiops sp., stranded on the coast of South Carolina, USA was found to be heavily infected in its intestine by tapeworms, which we identified molecularly. Sequencing of portions of the mitochondrial cytochrome c oxidase I (COI) and nuclear large subunit ribosomal RNA (28S rRNA) genes showed the cestodes to be Diphyllobothrium stemmacephalum, commonly known as a broad tapeworm. Infections of marine mammals by Diphyllobothrium have been previously reported in the Northwestern Atlantic Ocean, but only to genus level. Infection by tapeworms may be rare in dolphins in South Carolina, but because this species is zoonotic, its presence indicates the potential for an emerging public health concern.