Objective: To explore the effect of acupuncture on common extensor tendon (CET) thickness in patients with lateral epicondylitis (LE). Additionally, to identify whether clinical and ultrasonographic changes showed any correlation. Methods: Forty-one patients were randomly assigned to acupuncture and control groups. Conventional treatment (rest, NSA, bracing, exercise) methods for LE were applied to all patients. In addition to this, the acupuncture treatment was applied to the acupuncture group. The visual analog scale (VAS) for pain, the Duruoz Hand Index (DHI) for functioning of the affected limb, the pressure pain threshold, and CET thickness (via ultrasound imaging) were assessed before and end of the treatment in both groups. Results: The VAS and DHI scores in both groups decreased. The pressure pain threshold and CET thickness only demonstrated improvement in the acupuncture group. Conclusion: These findings show that the CET thickness was reduced after 10 sessions of acupuncture treatment in LE patients.