Public opinion surveys on American foreign policy often elicit many “don’t know” or “no opinion” responses. Researchers have paid surprisingly little attention to these responses, typically dropping them from their analyses or suppressing them in the survey design. We argue that these practices lead to potentially misleading conclusions about both the level of support for particular foreign policies and the determinants of individual attitudes. We demonstrate these problems using an original survey experiment testing the effect of including a DKNO option on three common questions about international trade, the use of force, and isolationism. Our findings also suggest that taking DKNO responses more seriously in our analyses provides a richer sense of the process through which important covariates actually influence attitudes.