This study evaluates the efficiency of the tax audit system in Türkiye after the structural reform using window analysis. The efficiency level of the system from 2011 to 2022 is calculated with input variables (number of audit staff and active taxpayers) and output variables (number of taxpayers audited and collection/accrual ratio). The results show that the system was efficient in 2011-2015 but declined in 2016-2022. Despite more audit personnel, the collection/accrual ratio did not improve. The study suggests ways to increase the system’s efficiency and provides insights for future research.