An infestation by the parasitic copepod Pennella balaenopterae was found in a stranded, 8-mo-old, female northern elephant seal (Mirounga angustirostris). Diagnosis was based on the finding of the cephalothoraxes of 14 adult female copepods from three subcutaneous sites. Bacteria cultured from lesion exudate included Arcanobacterium phocae, Escherichia coli, Edwardsiella tarda, an Enterococcus sp., and Proteus mirabilis. The lesions were drained and irrigated with chlorhexidine, and the seal was treated with a subcutaneous injection of ivermectin. The seal recovered and was released after 43 days.