The studies of the infestation state of the cod (Gadus morhua L.) by the Clavella adunca (Strøm, 1762) parasite were carried out in North Atlantic waters over the years 1970, 1974 and 1975. Totally 7168 cod specimens have been subjected to detailed ichthyological analysis, 4454 cods originating from Labrador and Newfoundland fishing grounds and 2714 from Spitsbergen Island fishing grounds. The results of observations of the parasite occurrence on the particular parts of cod body are presented in the work. The observations of differences in body-build proportions of female parasite and forms of bullae originating from different locations of attachment to the host were made as well. By the use of Student′s test t the significance of differences in infestation of cods from different regions was estimated.