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.