I examine whether corporate tax avoidance is associated with internal control weaknesses (ICWs) disclosed under the Sarbanes-Oxley Act (SOX). ICWs disclosed under SOX are frequently related to a firm's tax function. When pervasive ICWs exist, the likelihood increases that these frequent tax-related ICWs spill over from financial reporting issues to tax avoidance objectives. Thus, my research helps corporate stakeholders understand the implications of internal controls beyond simply financial reporting objectives. Results indicate that, on average, firms with a tax-related ICW have a 4 percent higher three-year cash effective tax rate relative to firms without any such weaknesses. Further estimates reveal that this negative relation stems from pervasive, company-level tax ICWs. Analysis of remediation suggests a causal link. I find that after remediating tax-related ICWs, firms report higher levels of tax avoidance in the future. Broadly, these findings support that internal control quality represents a proxy for internal governance, and thus the strength of alignment between managers and shareholders. Furthermore, tax-related internal controls represent an important underlying determinant of tax avoidance with significant cash flow effects, and implications beyond financial reporting. * Accepted by Lillan Mills. I am grateful for the helpful advice and suggestions of my dissertation committee: Jee-Hae Lim, Alan Macnaughton, Anindya Sen and especially my chair, Ken Klassen. I am also indebted to Tim Bauer, James Chyz, Cristi Gleason and Louise Hayes for their wonderful insight and assistance. This paper has also benefited greatly from the comments of Lillian Mills and two anonymous refereescause a effet. L'auteur constate qu'apr es avoir rem edi e aux DCI li ees a la fonction fiscale, les soci et es affichent ult erieurement des niveaux d'optimisation fiscale sup erieurs. De fac ßon g en erale, ces observations viennent etayer le fait que la qualit e du contrôle interne est une variable de substitution a la gouvernance interne et confirment donc l'ad equation des int erêts des gestionnaires et des actionnaires. Plus encore, les contrôles internes li es a la fonction fiscale sont un important d eterminant de l'optimisation fiscale qui a des r epercussions importantes sur les flux de tr esorerie et dont les cons equences d epassent l'information financi ere. 450 Contemporary Accounting Research CAR Vol. 33 No. 2 (Summer 2016)trols (COSO 2011)-and include weak risk management, lack of key personnel, inadequate communication, "tone at the top," etc. 3 While related to financial reporting of tax provisions, valuation allowances, and other reserves specifically, these ICWs could translate into missed tax-avoidance opportunities. Conversely, they could also reflect inaccurate evaluation of tax jurisdictions and other planning inputs yet to be discovered by tax authorities, or opportunities for management to extract rents. Consequently, I hypothesize that taxrelated ICWs reflect a lack of internal governance for the tax f...