This review is intended to increase awareness of the value of parasitological studies of the Atlantic cod, which has an exceptionally rich and varied parasite fauna compared with most other species of marine fish. We list 107 named species of protozoan and metazoan parasites recorded from cod, plus many that have been identified to generic or higher taxonomic levels only. This diversity is apparently linked to the omnivorous diet of cod, its occurrence at low salinities where it is exposed to infection by euryhaline parasites that most marine fish do not encounter, and its status as one of the most abundant and widespread piscivorous species in the North Atlantic. Parasitological studies of cod have been undertaken mainly in response to concerns about public health and spoilage effects of the more common and obvious parasites. We also review more academic aspects such as the host range and specificity of cod parasites, their life cycles, zoogeography, population dynamics and host sexual differences to parasitic infection. We also deal in depth with applied aspects such as the role of parasites as pathogens and their use as biological tags in population studies of cod and as indicators of marine pollution. We suggest areas in which further study is most urgently required and try to anticipate which parasites are likely to become important pathogens in the developing mariculture of cod. Copyright © 2001 Academic Press.