All 50 US states have enacted mandates requiring insurers to cover autism-related services. We assessed whether and to what extent variation in generosity of state insurance mandates has been associated with rate of growth in the health workforce for children with autism spectrum disorder: including board-certified behavioral analysts, child psychiatrists, and pediatricians. Drawing data from the National Conference of State Legislatures and Area Health Resource Files, we evaluated eight mandate policy features, utilizing a fixed-effect longitudinal regression framework to examine their relationships with workforce growth during a 15-year period (2003–2017) over which 44 states enacted a mandate. Aspects of mandate generosity included ages covered, spending caps, and types of services covered. We found that mandate generosity was closely associated with the magnitude of increase in supply of board-certified behavioral analysts and—to a lesser extent—child psychiatrists. States with the most generous mandates would be expected to have 39% more board-certified behavioral analysts and 17% more child psychiatrists in 2017, compared to states with least generous mandates. We found no association between mandate generosity and supply of pediatricians. Collectively, our results suggest that the degree of generosity afforded by mandates may be as important as the passage of mandate legislation itself for encouraging workforce growth. Lay abstract To improve access to health services for children with autism spectrum disorder, US states have passed laws requiring health insurers to cover autism-related care, commonly known as state insurance mandates. However, the features of mandates differ across states, with some state laws containing very generous provisions and others containing very restrictive provisions such as whether the mandates include children aged above 12 years, whether there is a limit on spending, and whether there are restrictions on the types of services covered. This study examined the relationship between generosity of mandates and growth in the health workforce between 2003 and 2017, a period during which 44 states passed mandates. We found that states that enacted more generous mandates experienced significantly more growth in board-certified behavioral analysts who provide behavioral therapy as well as more growth in child psychiatrists. We did not find differences in the growth of pediatricians, which is a less specialized segment of the workforce. Our findings were consistent across eight different mandate features and suggest that the content of legislation may be as important as whether or not legislation has been passed in terms of encouraging growth in the supply of services for children with autism spectrum disorder.