OBJECTIVES: To follow up anxiety in a cohort of women screened for breast cancer. METHODS: Within the framework of a pilot screening programme for breast cancer in the Canton of Vaud (Switzerland), a cohort of 924 participants aged 50-70 years were invited to answer questions on anxiety related to mammography screening. Anxiety was measured using a specific tool, the psychological consequences questionnaire (PCQ), and a new single item, direct question, breast cancer anxiety indicator (BCA). Participants were asked to fill in the questionnaire at four different phases: at screening, before the result, and 2 and 8 weeks after the result. The final response rate was 93.7%. Predictors of anxiety at each phase were assessed using multiple regression. RESULTS: Among those screening negative (94.7%), anxiety at screening was very low and remained so during the screening process. Among those screening false positive, anxiety was significantly higher 8 weeks after having received a negative diagnosis. Predictors of anxiety before screening were lower education and higher age, with a strong exogenous anxiety component. For subsequent phases, the initial anxiety score and education were the main determinants. Furthermore, a false positive result at screening was the most important predictor of anxiety 2 months after negative diagnosis. Anxiety measured with the BCA was strongly correlated with the PCQ. CONCLUSION: Anxiety was very low at screening and remained so during the process for negative women. Initial anxiety level was a strong predictor of anxiety during the entire process, up to 8 weeks after a negative result, and could be easily assessed using the BCA. The sustained higher anxiety level among those screening false positive is an undesirable side effect of the programme.