Objective To determine whether repeated 6-minute walk tests (6MWTs) are required for outcome measurement and exercise prescription in a typical cardiac rehabilitation (CR) population. Design Prospective longitudinal observational study. Setting Outpatient community health center. Participants Sixty-one of 154 consecutive patients. Intervention 6MWTs (N=2) were conducted at 3 assessment points: at CR start, postcompletion, and 6-months postcompletion. Main Outcome Measure 6MWT distance (6MWD). Results Mean 6MWD for the first (6MWT1) and second (6MWT2) 6MWTs at the 3 assessment points were 507ḵ (522Ḵ), 532Ḷ (560ḷ), and 549ṹ (575ᱰ7)m. Repeated 6MWDs strongly correlated at each assessment point, with intraclass correlation coefficients of .96 (95% confidence interval [CI], 0.93-.98), .97 (95% CI, .92-.98), and .94 (95% CI, .89-.97), respectively. Relative increases in mean 6MWD from 6MWT1 to 6MWT2 at each assessment point were 3%, 5%, and 5%, respectively (P<.001 in each case). Differences in walking speed derived from 6MWD1 and 6MWD2 did not translate into differences in exercise prescription. Conclusions The difference between 6MWD1 and 6MWD2 was consistent regardless of previous exposure to 6MWTs. A single 6MWT was as effective as 2 repeated 6MWTs for outcome measurement and exercise prescription. We therefore recommend that when 6MWDs are used for CR outcome measurement, either a single 6MWT be used or the number of 6MWTs performed be consistent at all assessment points.