A critical aspect of any audit examination is the study and evaluation of the client s internal control structure. Previous audit judgment research has concluded that auditors exhibit a great deal of inconsistency in their evaluations of internal control (Libby and Libby 1989; Ashton 1982; Libby 1981). Because of these inconsistencies, the need for decision aids to assist auditors in studying and evaluating internal control structure has been identified (Tubbs 1992; Libby and Frederick 1990; Libby and Libby 1989). However, inconsistent judgments have inhibited the development of these decision aids (Abdoimohammadi 1987), since it is difficult (if not impossible) to identify how various factors are considered by auditors in studying and evaluating internal control structure and assessing control risk. This paper illustrates the use of rough set theory to develop decision rules for evaluating a client s internal control structure. These decision rules are based on quot;expertquot; assessments of control risk after considering certain attributes (i.e., control procedures) surrounding the decision. The distinguishing feature of rough set theory is that any observed inconsistencies among experts can be explicitly incorporated into the decision rules. This feature is especially important for instances where uncertainties exist in various aspects of the decision (such as the study and evaluation of internal control structure). These decision rules may serve as the initial input into a decision aid that allows non-experts to make decision similar to those made by firm-wide experts.