This paper examines whether and why a sizable portion of eligible firms in Vietnam did not claim a 30-percent temporary corporate income tax reduction, part of a stimulus package to boost the economy during the Global Financial Crisis. Using census firm-level panel data supplemented with survey data collected for this study, I find that only 40–60 percent of eligible firms claimed the tax cut. This low take-up rate is surprising in the context of under-reporting behavior in which businesses try in many ways to reduce their tax liability. Using a difference-in-differences approach with firm-level fixed effects, I find that nonclaiming firms were either not aware of the policy or were afraid of a tax audit. The government’s policy may have boosted the economy by more had more firms known they could qualify for a tax cut.