ObjectiveTo user-test a web-based, interactive Option Grid decision aid ‘prostate-specific antigen (PSA) test: yes or no?’ to determine its usability, acceptability and feasibility with men of high and low health literacy.DesignA semi-structured interview study.SettingInterviews were conducted at a senior centre, academic hospital or college library in New Hampshire and Vermont.ParticipantsIndividuals over 45 years of age with no history of prostate cancer who voluntarily contacted study authors after viewing local invitations were eligible for inclusion. Twenty interviews were conducted: 10 participants had not completed a college degree, of which eight had low health literacy, and 10 participants had high health literacy.InterventionAn interactive, web-based Option Grid patient decision aid for considering whether or not to have a PSA test.ResultsUsers with lower health literacy levels were able to understand the content in the tool but were not able to navigate the Option Grid independent of assistance. The tool was used independently by men with high health literacy. In terms of acceptability, the flow of questions and answers embedded in the tool did not seem intuitive to some users who preferred seeing more risk information related to age and family history. Users envisioned that the tool could be feasibly implemented in clinical workflows.ConclusionMen in our sample with limited health literacy had difficulty navigating the Option Grid, thus suggesting that the tool was not appropriately designed to be usable by all audiences. The information provided in the tool is acceptable, but users preferred to view personalised risk information. Some participants could envision using this tool prior to an encounter in order to facilitate a better dialogue with their clinician.Ethics approvalThe study received ethical approval from the Dartmouth College Committee for the Protection of Human Subjects (STUDY00030116).