Past studies have generally found that perceptions of the likelihood of formal and informal sanctions have lower explanatory power of noncompliance with laws than do internalized norms. Using data from two telephone surveys, we examined a situational characteristic, structural opportunity, that may prod individuals to think about the likelihood of detection from the Internal Revenue Service for underreporting income. Structural opportunity is the degree to which an individual's economic or social situation provides ways to avoid detection. Individuals with high structural opportunity perceived a lower likelihood of IRS detection and indicated that they were less likely to feel guilty if they engaged in tax cheating. Our data also suggested that some individuals with high structural opportunity may be in social networks which condone tax cheating. As expected, structural opportunity provided a condition under which individuals took into consideration the perceived likelihood of formal and informal detection in formulating intentions to engage in tax cheating. Our findings suggest that an examination of the interaction between situational and individual characteristics will provide a more complete understanding of decisions to engage in illegal behavior. Implications for deterrence theory are discussed.