The present study investigated the relation between autistic traits and gender minority stress and the relative importance of autistic traits and gender minority stress in predicting mental health outcomes in gender minority adults. An online survey was completed by 90 transgender women, 72 transgender men, 48 non-binary individuals assigned male at birth (AMAB), and 98 non-binary individuals assigned female at birth (AFAB). Autistic traits positively correlated with internalised transphobia in the non-binary groups. In general, higher autistic traits and gender minority stress correlated with poorer mental health outcomes. After controlling for gender minority stress, autistic traits accounted for additional variance of suicidality across gender minority groups, anxiety symptoms in the non-binary groups, and all mental health outcomes in non-binary AFAB.