Autism spectrum disorder (ASDs), are pervasive, lifelong neurodevelopmental disorders. This potentially disabling disorder, has long been thought to primarily affect males. Recent research shows females are more often affected than previously assumed. ASD symptoms in females are often overlooked, because symptoms described and recognized in clinical practice are largely based on the male ASD phenotype. Compared to males, females with ASD show less peculiar preoccupations and have less restricted interests than men. Several studies have hypothesized that expectations connected to these gender roles may lead to more emphasis on adjustment of social behaviours in the upbringing of girls. This may contribute to the development of better (masking) communicative abilities in females with ASD than in their male counterparts. However, masking symptoms of autism, imitating socially acceptable behaviours of surrounding people, and assuming a strictly defined social role within different social contexts can be very tiring. Gender-related factors are therefore important predictors of health-related quality of life. Symptoms in females are not readily identified as ASD by current (male-biased) instruments and female-specific instruments do not yet exist. Poor understanding of female ASD phenotype and consequent diagnostic delay can lead to development of comorbid mental disorders, unexplained physical symptoms, lower quality of life, decreased participation in society, and higher societal costs. Large studies are needed to elucidate female ASD phenotypes in order to improve detection. This project focusses on initial concerns, symptoms, comorbidity and medication, using an unprecedented large clinical population of ASD patients (n=~2000) based on record review-methodology. It will include interviews and matched case-control studies and will lead to female specific adjustments of an existing validated screening instrument that will be freely available. We expect the project to gather valuable data to inform clinical practice which can lead to necessary diagnostic and therapeutic improvements for females with ASD.