BACKGROUND: Prior research examining autistic traits in gender minority adults has reported mixed findings. Most prior studies did not include non-binary individuals. Little is known about the mechanisms shaping autistic traits in gender minority adults. This study examined autistic traits, as well as constructs related to the extreme male brain theory of autism and the mindblindness theory, in transgender and non-binary adults. METHODS: An online survey was conducted to assess autism-related traits in 323 gender minority adults, including 74 transgender men (individuals assigned female at birth and identify as a man), 95 transgender women (individuals assigned male at birth and identify as a woman), 104 non-binary AFAB (individuals assigned female at birth and identify as non-binary), and 50 non-binary AMAB (individuals assigned male at birth and identify as non-binary). Autistic traits, systemising, empathising, and Theory of Mind (ToM) were measured using the Autism Spectrum Quotient (AQ), the short forms of the Systemising Quotient (SQ-Short) and the Empathy Quotient (EQ-Short), the 10-item version of the Empathy Quotient (EQ-10) and the Reading the Mind in the Eyes Test (Eyes Test). Participants' scores on these measures were compared with previously published scores based on large-scale general population samples including thousands of participants. RESULTS: On average, compared with control females in the general population samples, both transgender men and non-binary AFAB scored significantly higher on the AQ and the SQ-Short but scored significantly lower on the EQ-Short, the EQ-10, and the Eyes Test. No clear or consistent group differences emerged when transgender women and non-binary AMAB were compared with control males. LIMITATIONS: The present study does not have a large sample of gender minority adults. It has been argued that the measures employed may not provide a precise assessment of the psychological constructs of interest. The present study has a "non-clinical" sample. However, not all gender minorities have access to or require clinical services, and so a "non-clinical" sample may be more representative of the gender minority community as a whole than samples recruited through clinics. CONCLUSIONS: The current findings suggest a "masculinised" autism-related profile and reduced ToM in transgender men and in non-binary AFAB. These findings might be interpreted to support the extreme male brain theory of autism and the mindblindness theory. Further research is needed to corroborate these findings.