The use of stem-cell therapies for the treatment of various musculoskeletal conditions, especially knee osteoarthritis (OA), is rapidly expanding, despite only low-level evidence to support its use. Centers offering these therapies are often marketing and charging patients out-of-pocket costs for such services. Therefore, the purpose of this study was to determine the current marketed: (1) prices and (2) clinical efficacy of stem-cell therapies for knee OA. This was a prospective cross-sectional study which queried 317 U.S. centers that offered direct-to-consumer stem-cell therapies for musculoskeletal conditions. A total of 273 of 317 centers were successfully contacted via phone or e-mail, using a simulated 57-year-old male patient with knee OA. Scripted questions were asked by the simulated patient to determine the marketed prices and clinical efficacy. Centers generally reported the proportion of patients who had “good results” or “symptomatic improvement.” The mean price of a unilateral (same-day) stem-cell knee injection was $5,156 with a standard deviation of $2,446 (95% confidence interval [CI]: $4,550-5,762, n = 65). The mean proportion of claimed clinical efficacy was 82% with a standard deviation of 9.6% (95% CI: 79.0-85.5%, n = 36). Most American stem-cell centers offer therapies for knee OA. The cost of these therapies averages about $5,000 per injection, and centers claim that 80% of the patients had “good results” or “symptomatic improvement,” denoting a gap between what is documented in the published literature and the marketing claims. These findings offer both patients and physicians insight into the current stem-cell market for knee OA. We hope that with this information, providers can more optimally make patients aware of discrepancies between what is being marketed versus the current evidence-based landscape of these therapies for knee OA.