This paper documents how information technology (IT) impacts audit efforts. Using cross-sectional data on audit engagements for the 100 largest clients of an office of a leading international public accounting firm, it empirically evaluates the impact of the clients’ IT choices on their auditor’s audit effort. The results indicate that other things being equal, the higher level of automation or complexity a client’s IT exhibits, the more effort audit professionals exert for the engagement. On the other hand, the better control or support a client’s IT furnishes, the lower hours the audit team inputs into the engagement.