Cervical stiffness in horses is a common complaint and can adversely affect performance. Presenting signs may include resistance to turning, lameness not localized to the distal limb, poor performance, abnormal gait, loss of power, incoordination, and ataxia. The objective of this randomized, controlled, blinded study was to determine whether acupuncture (AP) can be an effective treatment for cervical stiffness in horses. Eighteen horses were randomly assigned to either the Test Group (acupuncture) or the Control Group (sham-acupuncture) with three treatments given 7-10 days apart. Lateral bend was quantitatively evaluated before the first treatment and one day after the third treatment with analysis on video recordings. Measurements were taken at the point of maximal bend (R1) and pre-compensation bend (R2). In addition, muscle mass of the neck was measured at the level of the caudal aspect of the second cervical vertebra and at the caudal aspect of the fifth cervical vertebra at the same assessment times as for lateral bend. The person taking the measurements was blinded as to treatment group. The results showed that the Test Group had significantly larger mean R1 (p = 0.019) and R2 (p = 0.008), than the Control Group. No significant difference was found in muscle mass between subject groups. These outcomes suggest that acupuncture can improve lateral bend in horses and can be an effective treatment for cervical stiffness in horses.