Objectives: To establish whether altered protocol characteristics of streamlined StepDown breast assessment clinics heightened or reduced the psychological distress of women in attendance compared with standard assessment. Willingness to attend future screening was also compared between the assessment groups. Design: Observational, prospective study of women attending either a mammogram-only StepDown or a standard breast assessment clinic. Women completed questionnaires on the day of assessment and 1 month later. Participants and setting: Women attending StepDown (136 women) or standard assessment clinics (148 women) at a BreastScreen centre between 10 November 2009 and 7 August 2010. Main outcome measures: Breast cancer worries; positive and negative psychological consequences of assessment (Psychological Consequences Questionnaire); breast cancer-related intrusion and avoidance (Impact of Event Scale); and willingness to attend, and uneasiness about, future screening. Results: At 1-month follow-up, no group differences were evident between those attending standard and StepDown clinics on breast cancer worries (P=0.44), positive (P =0.88) and negative (P =0.65) consequences, intrusion (P=0.64), and avoidance (P =0.87). Willingness to return for future mammograms was high, and did not differ between groups (P =0.16), although higher levels of unease were associated with lessened willingness to rescreen (P=0.04). Conclusions: There was no evidence that attending streamlined StepDown assessments had different outcomes in terms of distress than attending standard assessment clinics for women with a BreastScreen-detected abnormality. However, unease about attending future screening was generally associated with less willingness to do so in both groups; thus, there is a role for psycho-educational intervention to address these concerns.