Until the early twenty-first century, autism was primarily a condition diagnosed in boys, with a median ratio of four boys to one girl. Whether this is because there are more autistic boys than girls, or because autism is ‘missed’ more in girls, has been the subject of much debate. This chapter considers various explanations for the preponderance of male autistics: sex-linked genetic differences, greater variation in men for a range of traits, men’s greater susceptibility to infection and the effects of foetal testosterone. Since the 2010s, the balance has tipped towards examining the issue of missed diagnosis, which seems to be particularly acute for higher-functioning autistic women. This chapter considers three sub-narratives that might explain the missed-ness of women: the female autism phenotype, masking and the misdiagnosis of girls and women. I propose an alternative viewpoint to the-women-are-missed narrative: it is misleading to think women were previously ‘missed’, because the boundaries of autism have moved. Autism is more broadly defined in practice than it was in 1990 and the sub-narratives have both reflected and contributed to this broader concept.