Medicaid is a major insurer of autistic people. However, during the transition to adulthood, autistic individuals are more likely than people with intellectual disability to lose their Medicaid benefits. Individuals with intellectual disability may have greater success maintaining Medicaid coverage during this time because most states provide coverage to individuals with intellectual disability throughout adulthood, which is not the case for autism. Using national Medicaid data from 2008 to 2016, we estimated the probability of intellectual disability diagnosis accrual among autistic Medicaid beneficiaries. Medicaid beneficiaries ages 8 to 25 with 1+ inpatient or 2+ outpatient autism spectrum disorder claims, but no intellectual disability claim, in a 12-month eligibility period were included. We used a person-month discrete-time proportional hazards model. Disruptions in Medicaid coverage were operationalized as 2+ consecutive months of no coverage before coverage resumed (yes/no). One in five autistic individuals ages 8-25 accrued an intellectual disability diagnosis. The probability of accruing an intellectual disability diagnosis was higher among autistic individuals who had disruptions in Medicaid coverage compared to those without disruptions, and peaked at age 21 (during the transition to adulthood). Expanding Medicaid to cover autistic people of all ages could decrease the need for intellectual disability diagnosis accrual and improve health outcomes for autistic adults.