Abstract Objective—To develop a method for arthrocentesis of the temporomandibular joint in adult horses. Animals—7 equine cadaver heads and 6 clinically normal adult horses. Procedure—Fluoroscopy, contrast radiography, and computed tomography were used on cadaver specimens to locate the temporomandibular joint, identify externally palpable landmarks for joint access, guide needle placement into the joint, and illustrate regional anatomy. The arthrocentesis technique was performed on 6 live healthy adult horses to determine efficacy and safety of this procedure. Results—Externally palpable structures were identified as landmarks for temporomandibular arthrocentesis, including the lateral border of the condylar process of the mandible, the zygomatic process of the temporal bone, and the lateral pericapsular fat pad. Arthrocentesis was successful in all 6 joints in the live horses, and no complications developed. Conclusions and Clinical Relevance—The technique identified will improve the ability to examine and treat the temporomandibular joint in horses. (Am J Vet Res 2001;62:729–735).