Mustelids, including American mink (Neovison vison), are definitive hosts for sinus nematodes of the genus Skrjabingylus. Previous research has suggested that skrjabingylosis can cause a swelling of the frontal sinuses in mustelid hosts, leading to an inverse relationship between intensity of infection and braincase volume. We tested this hypothesis on 261 adult mink skulls collected in Ontario, Canada. Consistent with the hypothesis, we found a reduced slope in the relationship between skull size and braincase volume for male mink exhibiting lesions attributable to infection with Skrjabingylus, compared to male mink with no lesions. However, we found no differences in slope for female mink. Male mink with lesions also had shorter postorbital lengths and mastoid breadths compared to males without lesions. Our results demonstrated that sinus nematodes may cause reduced braincase volume, but only in male mink. Infection may also have broader effects on skull shape than localized damage to the frontal bones and braincase roof. We suggest that parasitism of mink by Skrjabingylus may be sex-biased because of the sexual size dimorphism of the species.