Introduction: Mindfulness interventions can improve a broad range of patient outcomes, but traditional mindfulness-based interventions are time and resource intensive. Emerging evidence indicates brief, single-session mindfulness interventions can also improve patient outcomes, and brief mindfulness interventions can be embedded into medical care pathways with minimal disruption. However, the direct impact of a brief mindfulness intervention on patients' pain while waiting in the clinic waiting room remains unexamined. Objective: A series of three, pilot, randomized controlled trials (RCTs) were conducted to examine the impact of a brief, audio-recorded, mindfulness intervention on patients' pain in the clinic waiting room. Method: Study 1 examined an 8-min mindfulness recording delivered before a provider visit; Study 2 examined a 5-min mindfulness recording after a provider visit; and Study 3 examined a 4-min mindfulness recording before a provider visit. Time- and attention-matched control conditions were used in each study. Studies 1 and 2 were conducted in an academic cancer hospital. Study 3 was conducted at a walk-in orthopedic clinic. Pain intensity was measured in each of the three studies. Anxiety and depression symptoms were measured in Studies 2 and 3. Pain unpleasantness was measured in Study 3. Results: A brief (i.e., 4- to 8-min), audio-recorded mindfulness intervention decreased patients' pain intensity in the clinic waiting room, whether delivered before (Study 1 Cohen's d=1.01, Study 3 Cohen's d=0.39) or after (Study 2 Cohen's d=0.89) a provider visit. Mindfulness had a significant effect on anxiety symptoms in both studies in which it was measured. No effect on depression symptoms was observed. Conclusions: Results from these three pilot RCTs indicate brief, audio-recorded, mindfulness interventions may be capable of quickly decreasing clinical symptoms. As such, embedding brief, audio-recorded, mindfulness interventions in clinic waiting rooms may have the potential to improve patient outcomes. The continued investigation of this intervention approach is needed. Clinical Trial Registrations: NCT04477278 and NCT06099964.