We describe the case of a 23-year-old woman with Gender Identity Disorder (GID) asking for a cross-sex hormonal treatment with sex reassignment surgery and who was recently diagnosed with Autism Spectrum Disorder (ASD). Gender identity clinics are now reporting an overrepresentation of individuals with ASD among GID patients. The prevalence of ASD is 10-fold higher among GID patients than in general population. However, few case reports or studies have explored the co-occurrence of ASD and GID. This co-occurrence is relevant for diagnostic and clinical management and also raises important theoretical issues.