OBJECTIVES: To determine the effect of adjusting colorectal-cancer (CRC) screening willingness-to-pay (WTP) estimates for uptake bias from yea-saying in a choice-format conjoint-analysis study.Yea-saying refers to a tendency to express agreement regardless of one’s actual views when responding to hypothetical questions.  Screening tests offer an opportunity to compare stated and actual uptake rates.   METHODS: Adults aged 45-70 years with no history of CRC and physicians from the United States and Canada completed a web-enabled choice-format conjoint survey that presented subjects with pairs of profiles for screening tests. Test features included test type, frequency, accuracy, and cost.  Each test-preference question was followed by a question asking if the respondent preferred no screening to the chosen test.  A bivariate probit model combined data from both questions. Predicted WTP conditional on purchasing a test and societal expected WTP adjusted for uptake probability were estimated for both samples. RESULTS: A total of 501 and 1,087 adults from Canada and the United States respectively, and 100 physicians from both countries completed the survey.  Patients opted for a screening test in about 70% of the questions.  Physicians expected their patients to opt for a screening only 50% of the time, which is the same as the observed uptake rate.  For any given screening test, physicians’ surrogate WTP values were significantly less than patients’ values. Moreover, patients had significantly larger divergences between conditional and expected WTP measures.  The US patient expected WTP for colonoscopy, adjusted for yea-saying bias in predicted uptake, was $435, which was 29% smaller than the unadjusted expected WTP. CONCLUSIONS: If stated-preference subjects choose testing more frequently than they would if actually offered the hypothetical alternatives, the upwardly biased uptake estimates distort societal WTP measures. Minimizing incentives for yea-saying, detecting potential bias, and adjusting resulting WTP estimates is a high priority for stated-preference research.