STUDY OBJECTIVES: To assess the psychological impact of mammographic screening on women with non-malignant outcomes after attending the Netherlands' National Breast Cancer Screening Programme. DESIGN: During one year all women with false positive test results (95) in a screening area were invited for the study. Each false positive was matched with two women with normal mammograms with respect to age and municipality. A random reference group of 400 was drawn from the female population in an area not yet included in the screening programme. Experiences with screening and psychological status of subjects were assessed 8-10 weeks after screening (T1) and again after six months (T2), by interviews as well as questionnaires. References completed two questionnaires with a six months' interval. PARTICIPANTS: 74 (78%) women with false positive outcomes and 113 (59%) women with negative outcomes participated at T1, of these 65 (88%) and 105 (93%) at T2, respectively; 238 references returned questionnaires at T1 (59%), of these 143 (60%) at T2. MAIN RESULTS: At 8-10 weeks after the screening, the women who received false positive test results scored higher on most of the variables indicating psychological disfunctioning than women with normal mammograms, but did not notably differ on the same variables from the non-screened reference group. Women with normal mammograms had the lowest scores on all the variables in the study at both assessments. The same situation was observed six months later. Although 61% of the women who received false positive mammograms reported that they had experienced the "false alarm" as a stressful event, this experience had apparently no adverse effects on their psychological functioning, as assessed 8-10 weeks after screening. CONCLUSIONS: Overall, breast screening is not likely to generate adverse psychological effects in "healthy" women, even if the outcome is false positive. Differences in psychological functioning between false positives and negatives are more likely ascribable to feelings of relief in the negative group than to raised anxiety and distress in the false positive group.