Gender nonconformity is substantially elevated in the autistic population, but the reasons for this are currently unclear. In a recent study, Kallitsounaki and Williams (Kallitsounaki and Williams, Journal of Autism and Developmental Disorders, 2020; authors 1 and 2 of the current paper) found significant relations between autistic traits and both gender dysphoric feelings and recalled cross-gender behaviour, and between mentalising ability and gender dysphoric feelings. The current study successfully replicated these findings (results were supplemented with Bayesian analyses), in sample of 126 adults. Furthermore, it extended the previous finding of the role of mentalising in the relation between autistic traits and gender dysphoric feelings, by showing that mentalising fully mediated this link. Results provide a potential partial explanation for the increased rate of gender nonconformity in the autistic population.