Mental health conditions are highly prevalent among autistic people, but an updated synthesis of sex-stratified prevalence data, contributing factors, and support strategies is lacking.To address this knowledge gap, we conducted a rapid review utilizing PRISMA-ScR guidelines. MEDLINE, CINAHL, and PsycINFO databases were searched for studies (2004-2024) including female participants with a clinical autism diagnosis, and with a focus on mental health. Of 8,420 records screened, 218 met inclusion criteria. An exploratory quantitative synthesis of population-based and registry-based studies revealed higher rates of mental health conditions in autistic females than males for anxiety, mood, eating, obsessive-compulsive, psychotic, and personality disorders. Narrative synthesis identified moderating factors, including sex-related physiology, gendered experiences, age, age at autism diagnosis, autism characteristics, and co-occurring conditions. Biological and social mechanisms likely interact as contributing factors. Severe consequences of poor mental health underscore the need for tailored approaches accounting for the specific profiles of autistic females.