Conflicting expert recommendations regarding cancer screening and prevention are growing in number, visibility, and importance, but their impact are not well understood. In this study, we examined the impact of conflicting recommendations about mammography screening on women's mammography behavior and perceptions. We conducted a secondary analysis of longitudinal data from the 1995 Maximizing Mammography Participation Trial, a large randomized interventional trial examining the effectiveness of patient reminders in increasing mammography utilization among women ages 50 to 79. Using the decision theory concept of "ambiguity" as an analytic framework, we tested several predictions about the effects of conflicting recommendations regarding mammography recommendations on behavior, cognitions, and emotions related to mammography screening. We found high perceived ambiguity about mammography recommendations to be associated with both diminished uptake of mammography over time [odds ratio (OR), 0.42; 95% confidence interval (95% CI), 0.23-0.76; P < 0.0001] and lower intentions for future mammography (OR, 0.34; 95% CI, 0.20-0.55; P < 0.0001). High perceived ambiguity also predicted greater mammography-related worry over time (OR, 2.60; 95% CI, 1.79-3.78; P < 0.0001). These findings suggest that conflicting recommendations regarding cancer screening and prevention have important effects, and we discuss the implications of these findings for future research.