The Ampullae of Lorenzini can vary in their size, shape and distribution patterns among elasmobranch species. However, no study has compared the ampullary characteristics between the sexes within a species. The present study found a sexual dimorphism in the Ampullae of Lorenzini of the lesser-spotted catshark, Scyliorhinus canicula. Male S. canicula were found to possess longer ampullae and alveoli, greater numbers of alveolar bulbs, larger sensory epithelial surface areas and greater numbers of sensory receptor cells in the ampullae than female S. canicula. Greater lengths of both ampullae and alveoli, numbers of alveoli, larger sensory epithelial surface areas and greater numbers of sensory receptor cells in male S. canicula could increase the capability of adult male S. canicula in detecting females. The presence of the sexual dimorphism in the alveoli of the Ampullae of Lorenzini could be directly related to reproductive behaviour and/or reflect the sexual segregation patterns of adult S. canicula.