Objective: The aim of this randomized controlled trial was to compare outcomes of standing vs seated mammography. Methods: Five hundred forty women were assessed for ease of getting into position, comfort and pain using visual analog scales. Blinded, independent assessment of film quality and length of time for the mammography procedure were additional outcomes. Results: Among women with previous experience of screening mammography, those who were seated had significantly less difficulty getting into position than those who stood, and they also reported less discomfort. There were no significant differences in these outcomes for the group of women having their first screening mammogram. There was no difference in reported pain between the seated and standing groups, either for first-time or experienced patients. For first-time patients there was a significantly higher percentage of inadequate films in the seated group compared with the standing group. There was no significant difference between groups in the duration of the procedure, either for first-time or experienced patients. Conclusion: In summary, there were benefits of sitting during mammography for women with previous experience of mammography in terms of improved ease of positioning and comfort. In terms of film quality, there were disadvantages associated with seated mammography for first-time patients, although these might not be clinically significant.